<?xml version="1.0" encoding="UTF-8"?>

<!--XBRL Document Created with the Workiva Platform-->
<!--Copyright 2026 Workiva-->
<!--r:6938ba0e-3605-41b9-bc2f-517c4bbeac52,g:d8768d54-d6f9-4635-9bbd-13c02f4acebd-->
<link:linkbase xmlns:link="http://www.xbrl.org/2003/linkbase" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xbrldt="http://xbrl.org/2005/xbrldt" xsi:schemaLocation="http://www.xbrl.org/2003/linkbase http://www.xbrl.org/2003/xbrl-linkbase-2003-12-31.xsd">
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/all" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#all"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#hypercube-dimension"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-default"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-domain"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/domain-member" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#domain-member"/>
  <link:roleRef roleURI="http://www.thefirst.com/role/ConsolidatedStatementsofIncomeandComprehensiveIncomeUnaudited" xlink:type="simple" xlink:href="fnlc-20260331.xsd#ConsolidatedStatementsofIncomeandComprehensiveIncomeUnaudited"/>
  <link:definitionLink xlink:role="http://www.thefirst.com/role/ConsolidatedStatementsofIncomeandComprehensiveIncomeUnaudited" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_70f7b3c5-858c-4cbb-9160-a9cd71f433d2" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_03aa58c4-8af9-49eb-89a0-5038b012510f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_70f7b3c5-858c-4cbb-9160-a9cd71f433d2" xlink:to="loc_us-gaap_StatementTable_03aa58c4-8af9-49eb-89a0-5038b012510f" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductOrServiceAxis_c9faee13-0178-4a1e-b526-47ce5a2bf5e4" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ProductOrServiceAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_03aa58c4-8af9-49eb-89a0-5038b012510f" xlink:to="loc_srt_ProductOrServiceAxis_c9faee13-0178-4a1e-b526-47ce5a2bf5e4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_c9faee13-0178-4a1e-b526-47ce5a2bf5e4_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ProductOrServiceAxis_c9faee13-0178-4a1e-b526-47ce5a2bf5e4" xlink:to="loc_srt_ProductsAndServicesDomain_c9faee13-0178-4a1e-b526-47ce5a2bf5e4_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_ef94939d-1d31-466d-94f2-07d8c2bc19ba" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ProductOrServiceAxis_c9faee13-0178-4a1e-b526-47ce5a2bf5e4" xlink:to="loc_srt_ProductsAndServicesDomain_ef94939d-1d31-466d-94f2-07d8c2bc19ba" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiduciaryAndTrustMember_0c0570bb-b427-48bf-93ba-4af1faac680a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiduciaryAndTrustMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_ef94939d-1d31-466d-94f2-07d8c2bc19ba" xlink:to="loc_us-gaap_FiduciaryAndTrustMember_0c0570bb-b427-48bf-93ba-4af1faac680a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DepositAccountMember_5e97dc85-19ce-4e1a-9cd7-2c3d94cecd2d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DepositAccountMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_ef94939d-1d31-466d-94f2-07d8c2bc19ba" xlink:to="loc_us-gaap_DepositAccountMember_5e97dc85-19ce-4e1a-9cd7-2c3d94cecd2d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MortgageBankingMember_bed7f9ec-9f86-492d-b884-4be31382b484" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_MortgageBankingMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_ef94939d-1d31-466d-94f2-07d8c2bc19ba" xlink:to="loc_us-gaap_MortgageBankingMember_bed7f9ec-9f86-492d-b884-4be31382b484" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebitCardMember_77e10d3f-1c71-4fd8-8c7a-a368fd67e23c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebitCardMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_ef94939d-1d31-466d-94f2-07d8c2bc19ba" xlink:to="loc_us-gaap_DebitCardMember_77e10d3f-1c71-4fd8-8c7a-a368fd67e23c" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestAndDividendIncomeOperatingAbstract_bb0b251c-67a2-476e-bf76-1d1af01e8a86" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_InterestAndDividendIncomeOperatingAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_70f7b3c5-858c-4cbb-9160-a9cd71f433d2" xlink:to="loc_us-gaap_InterestAndDividendIncomeOperatingAbstract_bb0b251c-67a2-476e-bf76-1d1af01e8a86" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestAndFeeIncomeLoansAndLeases_a3ca0a8b-68a7-439e-a3da-c75f16a3bcc8" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_InterestAndFeeIncomeLoansAndLeases"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InterestAndDividendIncomeOperatingAbstract_bb0b251c-67a2-476e-bf76-1d1af01e8a86" xlink:to="loc_us-gaap_InterestAndFeeIncomeLoansAndLeases_a3ca0a8b-68a7-439e-a3da-c75f16a3bcc8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestIncomeDepositsWithFinancialInstitutions_7c1142df-5969-43e7-b9d7-be6429648bd7" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_InterestIncomeDepositsWithFinancialInstitutions"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InterestAndDividendIncomeOperatingAbstract_bb0b251c-67a2-476e-bf76-1d1af01e8a86" xlink:to="loc_us-gaap_InterestIncomeDepositsWithFinancialInstitutions_7c1142df-5969-43e7-b9d7-be6429648bd7" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestAndDividendIncomeSecurities_a881fbad-ef35-4b9f-acb3-bb8c26bf2f4f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_InterestAndDividendIncomeSecurities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InterestAndDividendIncomeOperatingAbstract_bb0b251c-67a2-476e-bf76-1d1af01e8a86" xlink:to="loc_us-gaap_InterestAndDividendIncomeSecurities_a881fbad-ef35-4b9f-acb3-bb8c26bf2f4f" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestAndDividendIncomeOperating_30e504e2-dd26-4b53-928a-c79d52721ba8" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_InterestAndDividendIncomeOperating"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InterestAndDividendIncomeOperatingAbstract_bb0b251c-67a2-476e-bf76-1d1af01e8a86" xlink:to="loc_us-gaap_InterestAndDividendIncomeOperating_30e504e2-dd26-4b53-928a-c79d52721ba8" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestExpenseAbstract_b97baee2-e351-4b85-abbe-04573c12cc87" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_InterestExpenseAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_70f7b3c5-858c-4cbb-9160-a9cd71f433d2" xlink:to="loc_us-gaap_InterestExpenseAbstract_b97baee2-e351-4b85-abbe-04573c12cc87" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestExpenseDeposits_33f1be19-8109-4627-bee9-b5e65d7d4c67" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_InterestExpenseDeposits"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InterestExpenseAbstract_b97baee2-e351-4b85-abbe-04573c12cc87" xlink:to="loc_us-gaap_InterestExpenseDeposits_33f1be19-8109-4627-bee9-b5e65d7d4c67" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestExpenseBorrowings_73efaf60-7a53-4185-8b02-b56089352b6a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_InterestExpenseBorrowings"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InterestExpenseAbstract_b97baee2-e351-4b85-abbe-04573c12cc87" xlink:to="loc_us-gaap_InterestExpenseBorrowings_73efaf60-7a53-4185-8b02-b56089352b6a" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestExpenseOperating_8ed16022-a74a-4f77-8cc4-55a90510412d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_InterestExpenseOperating"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InterestExpenseAbstract_b97baee2-e351-4b85-abbe-04573c12cc87" xlink:to="loc_us-gaap_InterestExpenseOperating_8ed16022-a74a-4f77-8cc4-55a90510412d" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestIncomeExpenseNet_04ac77e9-7d2c-4f03-9730-1b60cdef819c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_InterestIncomeExpenseNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_70f7b3c5-858c-4cbb-9160-a9cd71f433d2" xlink:to="loc_us-gaap_InterestIncomeExpenseNet_04ac77e9-7d2c-4f03-9730-1b60cdef819c" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProvisionForLoanLossesExpensed_7d29f421-d864-41e2-8199-d181c931cdc1" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ProvisionForLoanLossesExpensed"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_70f7b3c5-858c-4cbb-9160-a9cd71f433d2" xlink:to="loc_us-gaap_ProvisionForLoanLossesExpensed_7d29f421-d864-41e2-8199-d181c931cdc1" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesHeldToMaturityCreditLossExpenseReversal_3d9313f5-2ac0-4913-ad29-8fdf23c1fa03" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtSecuritiesHeldToMaturityCreditLossExpenseReversal"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_70f7b3c5-858c-4cbb-9160-a9cd71f433d2" xlink:to="loc_us-gaap_DebtSecuritiesHeldToMaturityCreditLossExpenseReversal_3d9313f5-2ac0-4913-ad29-8fdf23c1fa03" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OffBalanceSheetCreditLossLiabilityCreditLossExpenseReversal_f11fc348-2a24-424b-9792-308842601818" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OffBalanceSheetCreditLossLiabilityCreditLossExpenseReversal"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_70f7b3c5-858c-4cbb-9160-a9cd71f433d2" xlink:to="loc_us-gaap_OffBalanceSheetCreditLossLiabilityCreditLossExpenseReversal_f11fc348-2a24-424b-9792-308842601818" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_fnlc_CreditLossExpenseReversal_ac0bbf14-4dad-487a-9fe3-0c2bebde3723" xlink:href="fnlc-20260331.xsd#fnlc_CreditLossExpenseReversal"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_70f7b3c5-858c-4cbb-9160-a9cd71f433d2" xlink:to="loc_fnlc_CreditLossExpenseReversal_ac0bbf14-4dad-487a-9fe3-0c2bebde3723" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestIncomeExpenseAfterProvisionForLoanLoss_f68d564b-53da-404b-87b1-423543548321" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_InterestIncomeExpenseAfterProvisionForLoanLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_70f7b3c5-858c-4cbb-9160-a9cd71f433d2" xlink:to="loc_us-gaap_InterestIncomeExpenseAfterProvisionForLoanLoss_f68d564b-53da-404b-87b1-423543548321" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NoninterestIncomeAbstract_7131e7d5-4af7-4303-9ed3-27d220aa8d23" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_NoninterestIncomeAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_70f7b3c5-858c-4cbb-9160-a9cd71f433d2" xlink:to="loc_us-gaap_NoninterestIncomeAbstract_7131e7d5-4af7-4303-9ed3-27d220aa8d23" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueFromContractWithCustomerIncludingAssessedTax_f1f16b9f-9688-4deb-85db-9c7555a2118e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RevenueFromContractWithCustomerIncludingAssessedTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NoninterestIncomeAbstract_7131e7d5-4af7-4303-9ed3-27d220aa8d23" xlink:to="loc_us-gaap_RevenueFromContractWithCustomerIncludingAssessedTax_f1f16b9f-9688-4deb-85db-9c7555a2118e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesAvailableForSaleRealizedGainLoss_019d7574-c3ed-713e-9332-e3a665ea312e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtSecuritiesAvailableForSaleRealizedGainLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NoninterestIncomeAbstract_7131e7d5-4af7-4303-9ed3-27d220aa8d23" xlink:to="loc_us-gaap_DebtSecuritiesAvailableForSaleRealizedGainLoss_019d7574-c3ed-713e-9332-e3a665ea312e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NoninterestIncomeOtherOperatingIncome_3d140e9b-b72c-422e-a989-d9cad40edf5b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_NoninterestIncomeOtherOperatingIncome"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NoninterestIncomeAbstract_7131e7d5-4af7-4303-9ed3-27d220aa8d23" xlink:to="loc_us-gaap_NoninterestIncomeOtherOperatingIncome_3d140e9b-b72c-422e-a989-d9cad40edf5b" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NoninterestIncome_595d77ea-787c-424e-b527-922a046175fc" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_NoninterestIncome"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NoninterestIncomeAbstract_7131e7d5-4af7-4303-9ed3-27d220aa8d23" xlink:to="loc_us-gaap_NoninterestIncome_595d77ea-787c-424e-b527-922a046175fc" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NoninterestExpenseAbstract_1cd88fa8-170b-432d-8eeb-ac2157b2386b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_NoninterestExpenseAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_70f7b3c5-858c-4cbb-9160-a9cd71f433d2" xlink:to="loc_us-gaap_NoninterestExpenseAbstract_1cd88fa8-170b-432d-8eeb-ac2157b2386b" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LaborAndRelatedExpense_92e554f8-29e2-4214-a77b-8bfb05ea9b18" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LaborAndRelatedExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NoninterestExpenseAbstract_1cd88fa8-170b-432d-8eeb-ac2157b2386b" xlink:to="loc_us-gaap_LaborAndRelatedExpense_92e554f8-29e2-4214-a77b-8bfb05ea9b18" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OccupancyNet_bb15c334-c0a0-4c3b-8f2d-87cb7bfa538d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OccupancyNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NoninterestExpenseAbstract_1cd88fa8-170b-432d-8eeb-ac2157b2386b" xlink:to="loc_us-gaap_OccupancyNet_bb15c334-c0a0-4c3b-8f2d-87cb7bfa538d" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquipmentExpense_0cb263a4-506a-49f7-97a7-ef152319d4a0" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EquipmentExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NoninterestExpenseAbstract_1cd88fa8-170b-432d-8eeb-ac2157b2386b" xlink:to="loc_us-gaap_EquipmentExpense_0cb263a4-506a-49f7-97a7-ef152319d4a0" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FederalDepositInsuranceCorporationPremiumExpense_66c553a7-9377-4940-b07a-fb49f6bf3b7e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FederalDepositInsuranceCorporationPremiumExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NoninterestExpenseAbstract_1cd88fa8-170b-432d-8eeb-ac2157b2386b" xlink:to="loc_us-gaap_FederalDepositInsuranceCorporationPremiumExpense_66c553a7-9377-4940-b07a-fb49f6bf3b7e" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AmortizationOfIntangibleAssets_7b697b5a-066a-45b2-88c2-0f4553480c59" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AmortizationOfIntangibleAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NoninterestExpenseAbstract_1cd88fa8-170b-432d-8eeb-ac2157b2386b" xlink:to="loc_us-gaap_AmortizationOfIntangibleAssets_7b697b5a-066a-45b2-88c2-0f4553480c59" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherNoninterestExpense_46ea6897-c2e6-4f2f-9e56-b2d2bca8ff6f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherNoninterestExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NoninterestExpenseAbstract_1cd88fa8-170b-432d-8eeb-ac2157b2386b" xlink:to="loc_us-gaap_OtherNoninterestExpense_46ea6897-c2e6-4f2f-9e56-b2d2bca8ff6f" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NoninterestExpense_e228d716-d5cf-4100-861e-9824b1c952f9" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_NoninterestExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NoninterestExpenseAbstract_1cd88fa8-170b-432d-8eeb-ac2157b2386b" xlink:to="loc_us-gaap_NoninterestExpense_e228d716-d5cf-4100-861e-9824b1c952f9" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest_48c330e7-74c8-4124-b37b-c7f2bbab6ebf" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_70f7b3c5-858c-4cbb-9160-a9cd71f433d2" xlink:to="loc_us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest_48c330e7-74c8-4124-b37b-c7f2bbab6ebf" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxExpenseBenefit_acb6e125-06bc-45ec-a85f-4d69cf6c4d15" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeTaxExpenseBenefit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_70f7b3c5-858c-4cbb-9160-a9cd71f433d2" xlink:to="loc_us-gaap_IncomeTaxExpenseBenefit_acb6e125-06bc-45ec-a85f-4d69cf6c4d15" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLoss_7f1dc240-7619-4244-aea8-393e0bdd2a08" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_NetIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_70f7b3c5-858c-4cbb-9160-a9cd71f433d2" xlink:to="loc_us-gaap_NetIncomeLoss_7f1dc240-7619-4244-aea8-393e0bdd2a08" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EarningsPerShareBasic_b37e5eb4-279a-4a3c-9480-01d788da6b7b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EarningsPerShareBasic"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_70f7b3c5-858c-4cbb-9160-a9cd71f433d2" xlink:to="loc_us-gaap_EarningsPerShareBasic_b37e5eb4-279a-4a3c-9480-01d788da6b7b" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EarningsPerShareDiluted_f856d983-6275-4800-a83d-8e3ead23f5f8" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EarningsPerShareDiluted"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_70f7b3c5-858c-4cbb-9160-a9cd71f433d2" xlink:to="loc_us-gaap_EarningsPerShareDiluted_f856d983-6275-4800-a83d-8e3ead23f5f8" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTaxPeriodIncreaseDecreaseAbstract_640309cf-aa4b-463f-b5db-003d0dc7dcde" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherComprehensiveIncomeLossNetOfTaxPeriodIncreaseDecreaseAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_70f7b3c5-858c-4cbb-9160-a9cd71f433d2" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTaxPeriodIncreaseDecreaseAbstract_640309cf-aa4b-463f-b5db-003d0dc7dcde" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodNetOfTax_123083b1-62c1-4154-ba8b-7889186d10a2" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTaxPeriodIncreaseDecreaseAbstract_640309cf-aa4b-463f-b5db-003d0dc7dcde" xlink:to="loc_us-gaap_OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodNetOfTax_123083b1-62c1-4154-ba8b-7889186d10a2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_fnlc_AvailableforsaleSecuritiesTransferredtoHeldtomaturitySecuritiesUnrealizedGainLoss_6345201e-f5e5-481e-bdda-db2f0ca9ba80" xlink:href="fnlc-20260331.xsd#fnlc_AvailableforsaleSecuritiesTransferredtoHeldtomaturitySecuritiesUnrealizedGainLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTaxPeriodIncreaseDecreaseAbstract_640309cf-aa4b-463f-b5db-003d0dc7dcde" xlink:to="loc_fnlc_AvailableforsaleSecuritiesTransferredtoHeldtomaturitySecuritiesUnrealizedGainLoss_6345201e-f5e5-481e-bdda-db2f0ca9ba80" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossBeforeReclassificationAfterTax_1af7c301-d04c-41d5-9d28-e00de323b527" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossBeforeReclassificationAfterTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTaxPeriodIncreaseDecreaseAbstract_640309cf-aa4b-463f-b5db-003d0dc7dcde" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossBeforeReclassificationAfterTax_1af7c301-d04c-41d5-9d28-e00de323b527" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent_30ac95b6-7cf0-41c0-9741-e8504de06da4" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTaxPeriodIncreaseDecreaseAbstract_640309cf-aa4b-463f-b5db-003d0dc7dcde" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent_30ac95b6-7cf0-41c0-9741-e8504de06da4" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ComprehensiveIncomeNetOfTax_df73ab4a-978d-4db4-92f2-599a898ebf19" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ComprehensiveIncomeNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_70f7b3c5-858c-4cbb-9160-a9cd71f433d2" xlink:to="loc_us-gaap_ComprehensiveIncomeNetOfTax_df73ab4a-978d-4db4-92f2-599a898ebf19" xlink:type="arc" order="16"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.thefirst.com/role/ConsolidatedStatementsofChangesinShareholdersEquityUnaudited" xlink:type="simple" xlink:href="fnlc-20260331.xsd#ConsolidatedStatementsofChangesinShareholdersEquityUnaudited"/>
  <link:definitionLink xlink:role="http://www.thefirst.com/role/ConsolidatedStatementsofChangesinShareholdersEquityUnaudited" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_bffd1552-b709-41d9-8406-a20954ce52dd" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_cc624c2b-e678-4dd2-94ae-aecebdc49d4d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_bffd1552-b709-41d9-8406-a20954ce52dd" xlink:to="loc_us-gaap_StatementTable_cc624c2b-e678-4dd2-94ae-aecebdc49d4d" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_58a15325-fd9b-4901-bb70-0633978e62c9" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementEquityComponentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_cc624c2b-e678-4dd2-94ae-aecebdc49d4d" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_58a15325-fd9b-4901-bb70-0633978e62c9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_58a15325-fd9b-4901-bb70-0633978e62c9_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_58a15325-fd9b-4901-bb70-0633978e62c9" xlink:to="loc_us-gaap_EquityComponentDomain_58a15325-fd9b-4901-bb70-0633978e62c9_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_b9a36b11-d98e-4975-b264-2880a3f27f9e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_58a15325-fd9b-4901-bb70-0633978e62c9" xlink:to="loc_us-gaap_EquityComponentDomain_b9a36b11-d98e-4975-b264-2880a3f27f9e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockIncludingAdditionalPaidInCapitalMember_045f9971-3be9-4b2b-b71f-ca3efa616b26" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CommonStockIncludingAdditionalPaidInCapitalMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_b9a36b11-d98e-4975-b264-2880a3f27f9e" xlink:to="loc_us-gaap_CommonStockIncludingAdditionalPaidInCapitalMember_045f9971-3be9-4b2b-b71f-ca3efa616b26" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetainedEarningsMember_0b133b76-3d53-45c9-a933-87ad1136c586" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RetainedEarningsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_b9a36b11-d98e-4975-b264-2880a3f27f9e" xlink:to="loc_us-gaap_RetainedEarningsMember_0b133b76-3d53-45c9-a933-87ad1136c586" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_983be463-f4ab-4049-ac7d-2c4b79e5640a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_b9a36b11-d98e-4975-b264-2880a3f27f9e" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_983be463-f4ab-4049-ac7d-2c4b79e5640a" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_825d5e16-d7ec-4240-ac18-bdb40b9ec931" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncreaseDecreaseInStockholdersEquityRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_bffd1552-b709-41d9-8406-a20954ce52dd" xlink:to="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_825d5e16-d7ec-4240-ac18-bdb40b9ec931" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesOutstanding_9b5ef15b-a338-4715-b2e1-ac5b5c34d86f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CommonStockSharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_825d5e16-d7ec-4240-ac18-bdb40b9ec931" xlink:to="loc_us-gaap_CommonStockSharesOutstanding_9b5ef15b-a338-4715-b2e1-ac5b5c34d86f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquity_ce26f0f8-4e76-45c6-bedc-2fefc6a102c4" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockholdersEquity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_825d5e16-d7ec-4240-ac18-bdb40b9ec931" xlink:to="loc_us-gaap_StockholdersEquity_ce26f0f8-4e76-45c6-bedc-2fefc6a102c4" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLoss_6a67d4f7-f6dd-46a9-be86-3c9127d3a9b1" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_NetIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_825d5e16-d7ec-4240-ac18-bdb40b9ec931" xlink:to="loc_us-gaap_NetIncomeLoss_6a67d4f7-f6dd-46a9-be86-3c9127d3a9b1" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodNetOfTax_da511f5e-40a2-4e9b-9ebb-cf69580b6c89" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_825d5e16-d7ec-4240-ac18-bdb40b9ec931" xlink:to="loc_us-gaap_OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodNetOfTax_da511f5e-40a2-4e9b-9ebb-cf69580b6c89" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_fnlc_AvailableforsaleSecuritiesTransferredtoHeldtomaturitySecuritiesUnrealizedGainLoss_b6755e71-b347-4d33-9a7b-2edaa60aa40a" xlink:href="fnlc-20260331.xsd#fnlc_AvailableforsaleSecuritiesTransferredtoHeldtomaturitySecuritiesUnrealizedGainLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_825d5e16-d7ec-4240-ac18-bdb40b9ec931" xlink:to="loc_fnlc_AvailableforsaleSecuritiesTransferredtoHeldtomaturitySecuritiesUnrealizedGainLoss_b6755e71-b347-4d33-9a7b-2edaa60aa40a" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossBeforeReclassificationAfterTax_4e262fdf-d64c-433a-ae9c-ffae3e97da87" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossBeforeReclassificationAfterTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_825d5e16-d7ec-4240-ac18-bdb40b9ec931" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossBeforeReclassificationAfterTax_4e262fdf-d64c-433a-ae9c-ffae3e97da87" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ComprehensiveIncomeNetOfTax_04f5efac-2268-4c68-87a7-453145df5ec9" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ComprehensiveIncomeNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_825d5e16-d7ec-4240-ac18-bdb40b9ec931" xlink:to="loc_us-gaap_ComprehensiveIncomeNetOfTax_04f5efac-2268-4c68-87a7-453145df5ec9" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DividendsCash_20b15853-461a-4e70-9836-9dd885d172c3" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DividendsCash"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_825d5e16-d7ec-4240-ac18-bdb40b9ec931" xlink:to="loc_us-gaap_DividendsCash_20b15853-461a-4e70-9836-9dd885d172c3" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue_bae9f4bc-ae61-4d04-ad87-e4a5388244a0" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_825d5e16-d7ec-4240-ac18-bdb40b9ec931" xlink:to="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue_bae9f4bc-ae61-4d04-ad87-e4a5388244a0" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockRepurchasedAndRetiredDuringPeriodShares_fea03d85-06c5-466a-b535-e912fea806bb" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockRepurchasedAndRetiredDuringPeriodShares"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_825d5e16-d7ec-4240-ac18-bdb40b9ec931" xlink:to="loc_us-gaap_StockRepurchasedAndRetiredDuringPeriodShares_fea03d85-06c5-466a-b535-e912fea806bb" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockRepurchasedAndRetiredDuringPeriodValue_72014599-4794-43b5-9150-98186a9038d1" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockRepurchasedAndRetiredDuringPeriodValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_825d5e16-d7ec-4240-ac18-bdb40b9ec931" xlink:to="loc_us-gaap_StockRepurchasedAndRetiredDuringPeriodValue_72014599-4794-43b5-9150-98186a9038d1" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesRestrictedStockAwardGross_ee6594b9-dcb5-4ed1-bf45-9e938b2bc545" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockIssuedDuringPeriodSharesRestrictedStockAwardGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_825d5e16-d7ec-4240-ac18-bdb40b9ec931" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesRestrictedStockAwardGross_ee6594b9-dcb5-4ed1-bf45-9e938b2bc545" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesNewIssues_f79f615d-29c2-441a-b323-87e783b58611" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockIssuedDuringPeriodSharesNewIssues"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_825d5e16-d7ec-4240-ac18-bdb40b9ec931" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesNewIssues_f79f615d-29c2-441a-b323-87e783b58611" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodValueNewIssues_768d4a0e-74c1-431a-8602-acec6af3d31f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockIssuedDuringPeriodValueNewIssues"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_825d5e16-d7ec-4240-ac18-bdb40b9ec931" xlink:to="loc_us-gaap_StockIssuedDuringPeriodValueNewIssues_768d4a0e-74c1-431a-8602-acec6af3d31f" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesOutstanding_2ddb0c8a-2829-4fa8-a74a-368122da3a51" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CommonStockSharesOutstanding"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquity_b8792500-3097-4962-9d07-1b563957879e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockholdersEquity"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.thefirst.com/role/InvestmentSecuritiesScheduleofAmortizedCostandEstimatedFairValueAFSHTMandRestrictedEquitySecuritiesDetails" xlink:type="simple" xlink:href="fnlc-20260331.xsd#InvestmentSecuritiesScheduleofAmortizedCostandEstimatedFairValueAFSHTMandRestrictedEquitySecuritiesDetails"/>
  <link:definitionLink xlink:role="http://www.thefirst.com/role/InvestmentSecuritiesScheduleofAmortizedCostandEstimatedFairValueAFSHTMandRestrictedEquitySecuritiesDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfHeldToMaturitySecuritiesLineItems_3010a1f2-589a-4f65-bb20-f4724fd2e004" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfHeldToMaturitySecuritiesLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfHeldToMaturitySecuritiesTable_c537517b-2de7-4221-bbb7-39ec96704e82" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfHeldToMaturitySecuritiesTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ScheduleOfHeldToMaturitySecuritiesLineItems_3010a1f2-589a-4f65-bb20-f4724fd2e004" xlink:to="loc_us-gaap_ScheduleOfHeldToMaturitySecuritiesTable_c537517b-2de7-4221-bbb7-39ec96704e82" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancialInstrumentAxis_6cefd897-e6db-4f1e-be52-e097104120f9" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FinancialInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfHeldToMaturitySecuritiesTable_c537517b-2de7-4221-bbb7-39ec96704e82" xlink:to="loc_us-gaap_FinancialInstrumentAxis_6cefd897-e6db-4f1e-be52-e097104120f9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_6cefd897-e6db-4f1e-be52-e097104120f9_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FinancialInstrumentAxis_6cefd897-e6db-4f1e-be52-e097104120f9" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_6cefd897-e6db-4f1e-be52-e097104120f9_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_367c6134-ccd7-4cd3-99ae-fe47c7008e9c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FinancialInstrumentAxis_6cefd897-e6db-4f1e-be52-e097104120f9" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_367c6134-ccd7-4cd3-99ae-fe47c7008e9c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_USTreasuryAndGovernmentMember_d51c220d-a57d-4caf-a80a-051b88299395" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_USTreasuryAndGovernmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_367c6134-ccd7-4cd3-99ae-fe47c7008e9c" xlink:to="loc_us-gaap_USTreasuryAndGovernmentMember_d51c220d-a57d-4caf-a80a-051b88299395" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MortgageBackedSecuritiesMember_fb10b423-a292-4831-b133-8c0284d75da0" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_MortgageBackedSecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_367c6134-ccd7-4cd3-99ae-fe47c7008e9c" xlink:to="loc_us-gaap_MortgageBackedSecuritiesMember_fb10b423-a292-4831-b133-8c0284d75da0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_USStatesAndPoliticalSubdivisionsMember_90516a27-3ec3-4201-b16f-1f28713217f5" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_USStatesAndPoliticalSubdivisionsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_367c6134-ccd7-4cd3-99ae-fe47c7008e9c" xlink:to="loc_us-gaap_USStatesAndPoliticalSubdivisionsMember_90516a27-3ec3-4201-b16f-1f28713217f5" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetBackedSecuritiesMember_69d1ee50-a83d-4a29-b1bf-395a33b984c2" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AssetBackedSecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_367c6134-ccd7-4cd3-99ae-fe47c7008e9c" xlink:to="loc_us-gaap_AssetBackedSecuritiesMember_69d1ee50-a83d-4a29-b1bf-395a33b984c2" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CorporateDebtSecuritiesMember_fe58c073-29b1-4008-b5c2-9a00ae1fcae5" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CorporateDebtSecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_367c6134-ccd7-4cd3-99ae-fe47c7008e9c" xlink:to="loc_us-gaap_CorporateDebtSecuritiesMember_fe58c073-29b1-4008-b5c2-9a00ae1fcae5" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleSecuritiesAbstract_76c78bfd-6a8a-4ae5-a2f1-f0efe7c51505" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AvailableForSaleSecuritiesAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfHeldToMaturitySecuritiesLineItems_3010a1f2-589a-4f65-bb20-f4724fd2e004" xlink:to="loc_us-gaap_AvailableForSaleSecuritiesAbstract_76c78bfd-6a8a-4ae5-a2f1-f0efe7c51505" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesAvailableForSaleAmortizedCostExcludingAccruedInterestAfterAllowanceForCreditLoss_88db14d8-f0f6-4b5b-a9b0-00cc56a299aa" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtSecuritiesAvailableForSaleAmortizedCostExcludingAccruedInterestAfterAllowanceForCreditLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AvailableForSaleSecuritiesAbstract_76c78bfd-6a8a-4ae5-a2f1-f0efe7c51505" xlink:to="loc_us-gaap_DebtSecuritiesAvailableForSaleAmortizedCostExcludingAccruedInterestAfterAllowanceForCreditLoss_88db14d8-f0f6-4b5b-a9b0-00cc56a299aa" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax_7dda9223-80a1-4521-a216-9ac8373cf385" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AvailableForSaleSecuritiesAbstract_76c78bfd-6a8a-4ae5-a2f1-f0efe7c51505" xlink:to="loc_us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax_7dda9223-80a1-4521-a216-9ac8373cf385" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax_234862f2-53db-4b90-913d-0e18fdb54a8d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AvailableForSaleSecuritiesAbstract_76c78bfd-6a8a-4ae5-a2f1-f0efe7c51505" xlink:to="loc_us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax_234862f2-53db-4b90-913d-0e18fdb54a8d" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesAvailableForSaleExcludingAccruedInterest_8ba0cacc-19a1-4adf-98c0-fa0e872b14b2" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtSecuritiesAvailableForSaleExcludingAccruedInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AvailableForSaleSecuritiesAbstract_76c78bfd-6a8a-4ae5-a2f1-f0efe7c51505" xlink:to="loc_us-gaap_DebtSecuritiesAvailableForSaleExcludingAccruedInterest_8ba0cacc-19a1-4adf-98c0-fa0e872b14b2" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HeldToMaturitySecuritiesAbstract_159acbe8-6570-4ae9-a8a8-588d6f85e0b7" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_HeldToMaturitySecuritiesAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfHeldToMaturitySecuritiesLineItems_3010a1f2-589a-4f65-bb20-f4724fd2e004" xlink:to="loc_us-gaap_HeldToMaturitySecuritiesAbstract_159acbe8-6570-4ae9-a8a8-588d6f85e0b7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesHeldToMaturityExcludingAccruedInterestBeforeAllowanceForCreditLoss_77508e38-61d5-48e6-b65f-5ab94daee7f8" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtSecuritiesHeldToMaturityExcludingAccruedInterestBeforeAllowanceForCreditLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_HeldToMaturitySecuritiesAbstract_159acbe8-6570-4ae9-a8a8-588d6f85e0b7" xlink:to="loc_us-gaap_DebtSecuritiesHeldToMaturityExcludingAccruedInterestBeforeAllowanceForCreditLoss_77508e38-61d5-48e6-b65f-5ab94daee7f8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HeldToMaturitySecuritiesAccumulatedUnrecognizedHoldingGain_5e5c69e3-273c-476e-acf4-b0bfd1031b76" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_HeldToMaturitySecuritiesAccumulatedUnrecognizedHoldingGain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_HeldToMaturitySecuritiesAbstract_159acbe8-6570-4ae9-a8a8-588d6f85e0b7" xlink:to="loc_us-gaap_HeldToMaturitySecuritiesAccumulatedUnrecognizedHoldingGain_5e5c69e3-273c-476e-acf4-b0bfd1031b76" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HeldToMaturitySecuritiesAccumulatedUnrecognizedHoldingLoss_21ee7bc9-63ee-46a7-a8e4-68772050610a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_HeldToMaturitySecuritiesAccumulatedUnrecognizedHoldingLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_HeldToMaturitySecuritiesAbstract_159acbe8-6570-4ae9-a8a8-588d6f85e0b7" xlink:to="loc_us-gaap_HeldToMaturitySecuritiesAccumulatedUnrecognizedHoldingLoss_21ee7bc9-63ee-46a7-a8e4-68772050610a" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HeldToMaturitySecuritiesFairValue_d4a36d3e-7d77-4b79-a6d6-551203e6a307" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_HeldToMaturitySecuritiesFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_HeldToMaturitySecuritiesAbstract_159acbe8-6570-4ae9-a8a8-588d6f85e0b7" xlink:to="loc_us-gaap_HeldToMaturitySecuritiesFairValue_d4a36d3e-7d77-4b79-a6d6-551203e6a307" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesHeldToMaturityAllowanceForCreditLossExcludingAccruedInterest_c4c39e4d-3ac3-4cac-98f6-f98598e9761f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtSecuritiesHeldToMaturityAllowanceForCreditLossExcludingAccruedInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_HeldToMaturitySecuritiesAbstract_159acbe8-6570-4ae9-a8a8-588d6f85e0b7" xlink:to="loc_us-gaap_DebtSecuritiesHeldToMaturityAllowanceForCreditLossExcludingAccruedInterest_c4c39e4d-3ac3-4cac-98f6-f98598e9761f" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesHeldToMaturityExcludingAccruedInterestAfterAllowanceForCreditLoss_e34473cb-9600-4b86-9a4c-94bcdc6d1d04" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtSecuritiesHeldToMaturityExcludingAccruedInterestAfterAllowanceForCreditLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_HeldToMaturitySecuritiesAbstract_159acbe8-6570-4ae9-a8a8-588d6f85e0b7" xlink:to="loc_us-gaap_DebtSecuritiesHeldToMaturityExcludingAccruedInterestAfterAllowanceForCreditLoss_e34473cb-9600-4b86-9a4c-94bcdc6d1d04" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquitySecuritiesRestrictedAbstract_95924753-2064-459f-8d76-0be7048f0225" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EquitySecuritiesRestrictedAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfHeldToMaturitySecuritiesLineItems_3010a1f2-589a-4f65-bb20-f4724fd2e004" xlink:to="loc_us-gaap_EquitySecuritiesRestrictedAbstract_95924753-2064-459f-8d76-0be7048f0225" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FederalHomeLoanBankStock_77bef5c2-d509-40bc-82a8-5c8993cd9636" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FederalHomeLoanBankStock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquitySecuritiesRestrictedAbstract_95924753-2064-459f-8d76-0be7048f0225" xlink:to="loc_us-gaap_FederalHomeLoanBankStock_77bef5c2-d509-40bc-82a8-5c8993cd9636" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FederalReserveBankStock_db62c034-a887-4068-a8f5-31d5c603bd41" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FederalReserveBankStock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquitySecuritiesRestrictedAbstract_95924753-2064-459f-8d76-0be7048f0225" xlink:to="loc_us-gaap_FederalReserveBankStock_db62c034-a887-4068-a8f5-31d5c603bd41" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FederalHomeLoanBankStockAndFederalReserveBankStock_f52e3265-556b-4b59-9feb-3e830d387177" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FederalHomeLoanBankStockAndFederalReserveBankStock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquitySecuritiesRestrictedAbstract_95924753-2064-459f-8d76-0be7048f0225" xlink:to="loc_us-gaap_FederalHomeLoanBankStockAndFederalReserveBankStock_f52e3265-556b-4b59-9feb-3e830d387177" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.thefirst.com/role/InvestmentSecuritiesNarrativeDetails" xlink:type="simple" xlink:href="fnlc-20260331.xsd#InvestmentSecuritiesNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.thefirst.com/role/InvestmentSecuritiesNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems_71e81d94-7980-492c-bc74-4652eceff514" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesAvailableForSaleTable_12f5925b-92b9-474f-9674-a185afdd5b77" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtSecuritiesAvailableForSaleTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems_71e81d94-7980-492c-bc74-4652eceff514" xlink:to="loc_us-gaap_DebtSecuritiesAvailableForSaleTable_12f5925b-92b9-474f-9674-a185afdd5b77" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancialInstrumentAxis_019d2908-70be-7976-bb86-e6f0e1f0e98d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FinancialInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtSecuritiesAvailableForSaleTable_12f5925b-92b9-474f-9674-a185afdd5b77" xlink:to="loc_us-gaap_FinancialInstrumentAxis_019d2908-70be-7976-bb86-e6f0e1f0e98d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019d2908-70be-7976-bb86-e6f0e1f0e98d_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FinancialInstrumentAxis_019d2908-70be-7976-bb86-e6f0e1f0e98d" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019d2908-70be-7976-bb86-e6f0e1f0e98d_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019d2908-70be-7a24-a097-f82421f775f6" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FinancialInstrumentAxis_019d2908-70be-7976-bb86-e6f0e1f0e98d" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019d2908-70be-7a24-a097-f82421f775f6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_fnlc_USTreasuryAndGovernmentAndCollateralizedMortgageBackedSecuritiesMember_019d2908-70be-7e1f-b5f8-fd7dd112c17a" xlink:href="fnlc-20260331.xsd#fnlc_USTreasuryAndGovernmentAndCollateralizedMortgageBackedSecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019d2908-70be-7a24-a097-f82421f775f6" xlink:to="loc_fnlc_USTreasuryAndGovernmentAndCollateralizedMortgageBackedSecuritiesMember_019d2908-70be-7e1f-b5f8-fd7dd112c17a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MunicipalBondsMember_019d2908-70be-713a-a99a-3eefb9ae61b9" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_MunicipalBondsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019d2908-70be-7a24-a097-f82421f775f6" xlink:to="loc_us-gaap_MunicipalBondsMember_019d2908-70be-713a-a99a-3eefb9ae61b9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CorporateDebtSecuritiesMember_019d2908-70be-7977-b65a-e98c3972185a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CorporateDebtSecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019d2908-70be-7a24-a097-f82421f775f6" xlink:to="loc_us-gaap_CorporateDebtSecuritiesMember_019d2908-70be-7977-b65a-e98c3972185a" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_USTreasuryAndGovernmentMember_019d2909-38bd-7a73-813e-a09050286f52" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_USTreasuryAndGovernmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019d2908-70be-7a24-a097-f82421f775f6" xlink:to="loc_us-gaap_USTreasuryAndGovernmentMember_019d2909-38bd-7a73-813e-a09050286f52" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CollateralAxis_019d2908-9ffc-7d10-af6a-0c7f8a24fb9c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CollateralAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtSecuritiesAvailableForSaleTable_12f5925b-92b9-474f-9674-a185afdd5b77" xlink:to="loc_us-gaap_CollateralAxis_019d2908-9ffc-7d10-af6a-0c7f8a24fb9c" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CollateralDomain_019d2908-9ffc-7d10-af6a-0c7f8a24fb9c_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CollateralDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_CollateralAxis_019d2908-9ffc-7d10-af6a-0c7f8a24fb9c" xlink:to="loc_us-gaap_CollateralDomain_019d2908-9ffc-7d10-af6a-0c7f8a24fb9c_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CollateralDomain_019d2908-9ffc-7e99-bcb0-e916c51460cf" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CollateralDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_CollateralAxis_019d2908-9ffc-7d10-af6a-0c7f8a24fb9c" xlink:to="loc_us-gaap_CollateralDomain_019d2908-9ffc-7e99-bcb0-e916c51460cf" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquitySecuritiesMember_019d2908-9ffc-7c67-a680-4958f7e383e7" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EquitySecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CollateralDomain_019d2908-9ffc-7e99-bcb0-e916c51460cf" xlink:to="loc_us-gaap_EquitySecuritiesMember_019d2908-9ffc-7c67-a680-4958f7e383e7" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesAvailableForSaleAmortizedCostAllowanceForCreditLossExcludingAccruedInterest_019d2908-70be-7a8d-8fb0-6ad70e4120ff" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtSecuritiesAvailableForSaleAmortizedCostAllowanceForCreditLossExcludingAccruedInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems_71e81d94-7980-492c-bc74-4652eceff514" xlink:to="loc_us-gaap_DebtSecuritiesAvailableForSaleAmortizedCostAllowanceForCreditLossExcludingAccruedInterest_019d2908-70be-7a8d-8fb0-6ad70e4120ff" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesHeldToMaturityAllowanceForCreditLossExcludingAccruedInterest_019d2908-70be-7261-bede-4b0ea3c095b0" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtSecuritiesHeldToMaturityAllowanceForCreditLossExcludingAccruedInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems_71e81d94-7980-492c-bc74-4652eceff514" xlink:to="loc_us-gaap_DebtSecuritiesHeldToMaturityAllowanceForCreditLossExcludingAccruedInterest_019d2908-70be-7261-bede-4b0ea3c095b0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_fnlc_NumberOfPrivateActivityBondsIssuedByWellKnownCustomers_019d2908-70be-79c8-b4c5-e7116db2f5ed" xlink:href="fnlc-20260331.xsd#fnlc_NumberOfPrivateActivityBondsIssuedByWellKnownCustomers"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems_71e81d94-7980-492c-bc74-4652eceff514" xlink:to="loc_fnlc_NumberOfPrivateActivityBondsIssuedByWellKnownCustomers_019d2908-70be-79c8-b4c5-e7116db2f5ed" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesHeldToMaturityExcludingAccruedInterestBeforeAllowanceForCreditLoss_019d2908-70be-711d-a4dc-0159103e396d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtSecuritiesHeldToMaturityExcludingAccruedInterestBeforeAllowanceForCreditLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems_71e81d94-7980-492c-bc74-4652eceff514" xlink:to="loc_us-gaap_DebtSecuritiesHeldToMaturityExcludingAccruedInterestBeforeAllowanceForCreditLoss_019d2908-70be-711d-a4dc-0159103e396d" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_fnlc_NumberOfIndividualCompaniesInBankingIndustry_019d2908-70be-70a5-b086-b79050af4d0e" xlink:href="fnlc-20260331.xsd#fnlc_NumberOfIndividualCompaniesInBankingIndustry"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems_71e81d94-7980-492c-bc74-4652eceff514" xlink:to="loc_fnlc_NumberOfIndividualCompaniesInBankingIndustry_019d2908-70be-70a5-b086-b79050af4d0e" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesAvailableForSaleRestricted_019d2908-9ffc-7189-b6d0-2c82497f4a32" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtSecuritiesAvailableForSaleRestricted"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems_71e81d94-7980-492c-bc74-4652eceff514" xlink:to="loc_us-gaap_DebtSecuritiesAvailableForSaleRestricted_019d2908-9ffc-7189-b6d0-2c82497f4a32" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_fnlc_NumberOfSecuritiesTemporarilyImpaired_019d2908-ba5d-725c-ae7d-e225a36bd602" xlink:href="fnlc-20260331.xsd#fnlc_NumberOfSecuritiesTemporarilyImpaired"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems_71e81d94-7980-492c-bc74-4652eceff514" xlink:to="loc_fnlc_NumberOfSecuritiesTemporarilyImpaired_019d2908-ba5d-725c-ae7d-e225a36bd602" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableThresholdPeriodPastDue_019d2909-38bd-7679-a5d4-a19173269e8c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FinancingReceivableThresholdPeriodPastDue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems_71e81d94-7980-492c-bc74-4652eceff514" xlink:to="loc_us-gaap_FinancingReceivableThresholdPeriodPastDue_019d2909-38bd-7679-a5d4-a19173269e8c" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesHeldToMaturityNonaccrual_019d2909-38bd-78f9-be98-91b210281d0d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtSecuritiesHeldToMaturityNonaccrual"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems_71e81d94-7980-492c-bc74-4652eceff514" xlink:to="loc_us-gaap_DebtSecuritiesHeldToMaturityNonaccrual_019d2909-38bd-78f9-be98-91b210281d0d" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_fnlc_AvailableforSaleSecuritiesTransferredSecurityatCarryingValue_019d2909-38bd-7e50-b85e-914bdb5dd148" xlink:href="fnlc-20260331.xsd#fnlc_AvailableforSaleSecuritiesTransferredSecurityatCarryingValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems_71e81d94-7980-492c-bc74-4652eceff514" xlink:to="loc_fnlc_AvailableforSaleSecuritiesTransferredSecurityatCarryingValue_019d2909-38bd-7e50-b85e-914bdb5dd148" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_fnlc_AvailableforSaleSecuritiesTransferredSecurityatFairValue_019d2909-38bd-76d7-90a3-32a661c8eadc" xlink:href="fnlc-20260331.xsd#fnlc_AvailableforSaleSecuritiesTransferredSecurityatFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems_71e81d94-7980-492c-bc74-4652eceff514" xlink:to="loc_fnlc_AvailableforSaleSecuritiesTransferredSecurityatFairValue_019d2909-38bd-76d7-90a3-32a661c8eadc" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_fnlc_AvailableforsaleSecuritiesTransferredtoHeldtomaturitySecuritiesAccumulatedUnrealizedGainLoss_019d2909-38bd-7f28-84f3-b83b6907babf" xlink:href="fnlc-20260331.xsd#fnlc_AvailableforsaleSecuritiesTransferredtoHeldtomaturitySecuritiesAccumulatedUnrealizedGainLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems_71e81d94-7980-492c-bc74-4652eceff514" xlink:to="loc_fnlc_AvailableforsaleSecuritiesTransferredtoHeldtomaturitySecuritiesAccumulatedUnrealizedGainLoss_019d2909-38bd-7f28-84f3-b83b6907babf" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_fnlc_OtherComprehensiveIncomeLossAccumulatedUnrealizedGainLossonTransferofAvailableforsaleSecuritiestoHeldtomaturity_019d2909-5896-74dc-93d4-ebc238f369e5" xlink:href="fnlc-20260331.xsd#fnlc_OtherComprehensiveIncomeLossAccumulatedUnrealizedGainLossonTransferofAvailableforsaleSecuritiestoHeldtomaturity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems_71e81d94-7980-492c-bc74-4652eceff514" xlink:to="loc_fnlc_OtherComprehensiveIncomeLossAccumulatedUnrealizedGainLossonTransferofAvailableforsaleSecuritiestoHeldtomaturity_019d2909-5896-74dc-93d4-ebc238f369e5" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_fnlc_NumberOfStatesInNewEnglandWhereFhlbServe_019d2909-5896-7a36-a5b1-d9ed0a73d4ce" xlink:href="fnlc-20260331.xsd#fnlc_NumberOfStatesInNewEnglandWhereFhlbServe"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems_71e81d94-7980-492c-bc74-4652eceff514" xlink:to="loc_fnlc_NumberOfStatesInNewEnglandWhereFhlbServe_019d2909-5896-7a36-a5b1-d9ed0a73d4ce" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FederalHomeLoanBankStock_019d2909-5896-75a6-a85c-36223958e1d0" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FederalHomeLoanBankStock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems_71e81d94-7980-492c-bc74-4652eceff514" xlink:to="loc_us-gaap_FederalHomeLoanBankStock_019d2909-5896-75a6-a85c-36223958e1d0" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FederalReserveBankStock_019d2909-5896-7deb-8a44-b0ce912e4af5" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FederalReserveBankStock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems_71e81d94-7980-492c-bc74-4652eceff514" xlink:to="loc_us-gaap_FederalReserveBankStock_019d2909-5896-7deb-8a44-b0ce912e4af5" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_fnlc_RestrictedEquitySecuritiesUnrealizedLosses_019d2909-5896-73df-85b5-cc5e8887735a" xlink:href="fnlc-20260331.xsd#fnlc_RestrictedEquitySecuritiesUnrealizedLosses"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems_71e81d94-7980-492c-bc74-4652eceff514" xlink:to="loc_fnlc_RestrictedEquitySecuritiesUnrealizedLosses_019d2909-5896-73df-85b5-cc5e8887735a" xlink:type="arc" order="16"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.thefirst.com/role/InvestmentSecuritiesSecuritiesTemporarilyImpairedDetails" xlink:type="simple" xlink:href="fnlc-20260331.xsd#InvestmentSecuritiesSecuritiesTemporarilyImpairedDetails"/>
  <link:definitionLink xlink:role="http://www.thefirst.com/role/InvestmentSecuritiesSecuritiesTemporarilyImpairedDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems_3abe9a7b-7db1-4b91-8739-c80648a53fdb" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesAvailableForSaleTable_3b1e653c-1373-4e0e-a1e5-20634a952bc3" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtSecuritiesAvailableForSaleTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems_3abe9a7b-7db1-4b91-8739-c80648a53fdb" xlink:to="loc_us-gaap_DebtSecuritiesAvailableForSaleTable_3b1e653c-1373-4e0e-a1e5-20634a952bc3" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancialInstrumentAxis_9f7e261c-4a08-429c-a3f8-b9f047cf8b6a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FinancialInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtSecuritiesAvailableForSaleTable_3b1e653c-1373-4e0e-a1e5-20634a952bc3" xlink:to="loc_us-gaap_FinancialInstrumentAxis_9f7e261c-4a08-429c-a3f8-b9f047cf8b6a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_9f7e261c-4a08-429c-a3f8-b9f047cf8b6a_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FinancialInstrumentAxis_9f7e261c-4a08-429c-a3f8-b9f047cf8b6a" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_9f7e261c-4a08-429c-a3f8-b9f047cf8b6a_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_7eea03ec-feef-4c2c-a79d-e427c640dcc6" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FinancialInstrumentAxis_9f7e261c-4a08-429c-a3f8-b9f047cf8b6a" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_7eea03ec-feef-4c2c-a79d-e427c640dcc6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_USTreasuryAndGovernmentMember_7d0b683e-bf51-41b4-be97-6b17f6593198" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_USTreasuryAndGovernmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_7eea03ec-feef-4c2c-a79d-e427c640dcc6" xlink:to="loc_us-gaap_USTreasuryAndGovernmentMember_7d0b683e-bf51-41b4-be97-6b17f6593198" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MortgageBackedSecuritiesMember_0657311f-ce4b-400b-a364-dfb2a2fd9af8" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_MortgageBackedSecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_7eea03ec-feef-4c2c-a79d-e427c640dcc6" xlink:to="loc_us-gaap_MortgageBackedSecuritiesMember_0657311f-ce4b-400b-a364-dfb2a2fd9af8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_USStatesAndPoliticalSubdivisionsMember_8bdd3afd-27d4-4a70-ab1e-ba91480db9b1" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_USStatesAndPoliticalSubdivisionsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_7eea03ec-feef-4c2c-a79d-e427c640dcc6" xlink:to="loc_us-gaap_USStatesAndPoliticalSubdivisionsMember_8bdd3afd-27d4-4a70-ab1e-ba91480db9b1" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetBackedSecuritiesMember_8fc383e4-3ec9-4756-8f17-a7f829ab9430" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AssetBackedSecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_7eea03ec-feef-4c2c-a79d-e427c640dcc6" xlink:to="loc_us-gaap_AssetBackedSecuritiesMember_8fc383e4-3ec9-4756-8f17-a7f829ab9430" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12Months_04368e88-b4fa-4460-9bc9-29e8125902a8" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12Months"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems_3abe9a7b-7db1-4b91-8739-c80648a53fdb" xlink:to="loc_us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12Months_04368e88-b4fa-4460-9bc9-29e8125902a8" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss_f8bfbc24-dcf0-4187-bad9-84ff2898dcc8" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems_3abe9a7b-7db1-4b91-8739-c80648a53fdb" xlink:to="loc_us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss_f8bfbc24-dcf0-4187-bad9-84ff2898dcc8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLonger_2477f866-89c1-49fa-937a-c7a57f6166cd" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLonger"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems_3abe9a7b-7db1-4b91-8739-c80648a53fdb" xlink:to="loc_us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLonger_2477f866-89c1-49fa-937a-c7a57f6166cd" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss_e38703dc-6149-40de-a7cd-dc6c255f47e1" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems_3abe9a7b-7db1-4b91-8739-c80648a53fdb" xlink:to="loc_us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss_e38703dc-6149-40de-a7cd-dc6c255f47e1" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesAvailableForSaleUnrealizedLossPosition_9d800aad-9acb-4f04-b3b3-b69f84af6216" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtSecuritiesAvailableForSaleUnrealizedLossPosition"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems_3abe9a7b-7db1-4b91-8739-c80648a53fdb" xlink:to="loc_us-gaap_DebtSecuritiesAvailableForSaleUnrealizedLossPosition_9d800aad-9acb-4f04-b3b3-b69f84af6216" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesAvailableForSaleUnrealizedLossPositionAccumulatedLoss_0e8d0c63-599c-4660-9914-43a6cd2fdb49" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtSecuritiesAvailableForSaleUnrealizedLossPositionAccumulatedLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems_3abe9a7b-7db1-4b91-8739-c80648a53fdb" xlink:to="loc_us-gaap_DebtSecuritiesAvailableForSaleUnrealizedLossPositionAccumulatedLoss_0e8d0c63-599c-4660-9914-43a6cd2fdb49" xlink:type="arc" order="5"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.thefirst.com/role/InvestmentSecuritiesDebtSecuritiesHeldtoMaturityAllowanceforCreditLossDetails" xlink:type="simple" xlink:href="fnlc-20260331.xsd#InvestmentSecuritiesDebtSecuritiesHeldtoMaturityAllowanceforCreditLossDetails"/>
  <link:definitionLink xlink:role="http://www.thefirst.com/role/InvestmentSecuritiesDebtSecuritiesHeldtoMaturityAllowanceforCreditLossDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesHeldtomaturityAllowanceForCreditLossLineItems_13083b44-3f23-4dd3-8a9a-d45b1cba2c37" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtSecuritiesHeldtomaturityAllowanceForCreditLossLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesHeldToMaturityAllowanceForCreditLossTable_d826be7e-b9e0-434b-aaaa-f31c878cfe8d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtSecuritiesHeldToMaturityAllowanceForCreditLossTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DebtSecuritiesHeldtomaturityAllowanceForCreditLossLineItems_13083b44-3f23-4dd3-8a9a-d45b1cba2c37" xlink:to="loc_us-gaap_DebtSecuritiesHeldToMaturityAllowanceForCreditLossTable_d826be7e-b9e0-434b-aaaa-f31c878cfe8d" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancialInstrumentAxis_eb2ed832-a873-4cd1-96d8-2f37480d863a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FinancialInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtSecuritiesHeldToMaturityAllowanceForCreditLossTable_d826be7e-b9e0-434b-aaaa-f31c878cfe8d" xlink:to="loc_us-gaap_FinancialInstrumentAxis_eb2ed832-a873-4cd1-96d8-2f37480d863a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_eb2ed832-a873-4cd1-96d8-2f37480d863a_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FinancialInstrumentAxis_eb2ed832-a873-4cd1-96d8-2f37480d863a" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_eb2ed832-a873-4cd1-96d8-2f37480d863a_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_c74fea23-bb30-4a81-b18b-428b420ce5d7" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FinancialInstrumentAxis_eb2ed832-a873-4cd1-96d8-2f37480d863a" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_c74fea23-bb30-4a81-b18b-428b420ce5d7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_USStatesAndPoliticalSubdivisionsMember_4865d7a2-df60-44ae-ba6e-5de666e5e8c6" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_USStatesAndPoliticalSubdivisionsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_c74fea23-bb30-4a81-b18b-428b420ce5d7" xlink:to="loc_us-gaap_USStatesAndPoliticalSubdivisionsMember_4865d7a2-df60-44ae-ba6e-5de666e5e8c6" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CorporateDebtSecuritiesMember_7defd622-d84c-4530-b81e-500413b4d01a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CorporateDebtSecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_c74fea23-bb30-4a81-b18b-428b420ce5d7" xlink:to="loc_us-gaap_CorporateDebtSecuritiesMember_7defd622-d84c-4530-b81e-500413b4d01a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesHeldToMaturityAllowanceForCreditLossRollForward_2d272873-3a4e-4bb6-9302-7822334d4471" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtSecuritiesHeldToMaturityAllowanceForCreditLossRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtSecuritiesHeldtomaturityAllowanceForCreditLossLineItems_13083b44-3f23-4dd3-8a9a-d45b1cba2c37" xlink:to="loc_us-gaap_DebtSecuritiesHeldToMaturityAllowanceForCreditLossRollForward_2d272873-3a4e-4bb6-9302-7822334d4471" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesHeldToMaturityAllowanceForCreditLossExcludingAccruedInterest_cb73e7e9-946e-49de-8fcd-9e8babc097b8" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtSecuritiesHeldToMaturityAllowanceForCreditLossExcludingAccruedInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtSecuritiesHeldToMaturityAllowanceForCreditLossRollForward_2d272873-3a4e-4bb6-9302-7822334d4471" xlink:to="loc_us-gaap_DebtSecuritiesHeldToMaturityAllowanceForCreditLossExcludingAccruedInterest_cb73e7e9-946e-49de-8fcd-9e8babc097b8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesHeldToMaturityExcludingAccruedInterestCreditLossExpenseReversal_27305778-b119-444b-bd3c-7919f238df4e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtSecuritiesHeldToMaturityExcludingAccruedInterestCreditLossExpenseReversal"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtSecuritiesHeldToMaturityAllowanceForCreditLossRollForward_2d272873-3a4e-4bb6-9302-7822334d4471" xlink:to="loc_us-gaap_DebtSecuritiesHeldToMaturityExcludingAccruedInterestCreditLossExpenseReversal_27305778-b119-444b-bd3c-7919f238df4e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesHeldToMaturityExcludingAccruedInterestAllowanceForCreditLossWriteoff_a8ac42a5-652a-466b-9620-1ba15360b4a9" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtSecuritiesHeldToMaturityExcludingAccruedInterestAllowanceForCreditLossWriteoff"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtSecuritiesHeldToMaturityAllowanceForCreditLossRollForward_2d272873-3a4e-4bb6-9302-7822334d4471" xlink:to="loc_us-gaap_DebtSecuritiesHeldToMaturityExcludingAccruedInterestAllowanceForCreditLossWriteoff_a8ac42a5-652a-466b-9620-1ba15360b4a9" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesHeldToMaturityExcludingAccruedInterestAllowanceForCreditLossRecovery_f2128d6a-ccb2-4d45-b721-345512be5fb0" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtSecuritiesHeldToMaturityExcludingAccruedInterestAllowanceForCreditLossRecovery"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtSecuritiesHeldToMaturityAllowanceForCreditLossRollForward_2d272873-3a4e-4bb6-9302-7822334d4471" xlink:to="loc_us-gaap_DebtSecuritiesHeldToMaturityExcludingAccruedInterestAllowanceForCreditLossRecovery_f2128d6a-ccb2-4d45-b721-345512be5fb0" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesHeldToMaturityAllowanceForCreditLossExcludingAccruedInterest_0d9bce53-076c-4fdd-a836-2c91ba9b8732" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtSecuritiesHeldToMaturityAllowanceForCreditLossExcludingAccruedInterest"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.thefirst.com/role/LoansLoanPortfolioDetails" xlink:type="simple" xlink:href="fnlc-20260331.xsd#LoansLoanPortfolioDetails"/>
  <link:definitionLink xlink:role="http://www.thefirst.com/role/LoansLoanPortfolioDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccountsNotesAndLoansReceivableLineItems_df963865-7ba1-4d98-8cf8-9b59bf7da4f5" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AccountsNotesAndLoansReceivableLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfAccountsNotesLoansAndFinancingReceivableTable_ec120f49-b6e4-4a79-8adf-37831256e5a6" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfAccountsNotesLoansAndFinancingReceivableTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_AccountsNotesAndLoansReceivableLineItems_df963865-7ba1-4d98-8cf8-9b59bf7da4f5" xlink:to="loc_us-gaap_ScheduleOfAccountsNotesLoansAndFinancingReceivableTable_ec120f49-b6e4-4a79-8adf-37831256e5a6" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivablePortfolioSegmentAxis_80b53f74-6b41-4a33-845d-242e6ae7dea3" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FinancingReceivablePortfolioSegmentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfAccountsNotesLoansAndFinancingReceivableTable_ec120f49-b6e4-4a79-8adf-37831256e5a6" xlink:to="loc_us-gaap_FinancingReceivablePortfolioSegmentAxis_80b53f74-6b41-4a33-845d-242e6ae7dea3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_80b53f74-6b41-4a33-845d-242e6ae7dea3_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FinancingReceivablePortfolioSegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FinancingReceivablePortfolioSegmentAxis_80b53f74-6b41-4a33-845d-242e6ae7dea3" xlink:to="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_80b53f74-6b41-4a33-845d-242e6ae7dea3_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_b353f852-b2c8-482e-9549-2cf9ba28f3e4" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FinancingReceivablePortfolioSegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FinancingReceivablePortfolioSegmentAxis_80b53f74-6b41-4a33-845d-242e6ae7dea3" xlink:to="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_b353f852-b2c8-482e-9549-2cf9ba28f3e4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommercialPortfolioSegmentMember_cdc4f155-6a1f-430b-8e30-3276091726e9" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CommercialPortfolioSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_b353f852-b2c8-482e-9549-2cf9ba28f3e4" xlink:to="loc_us-gaap_CommercialPortfolioSegmentMember_cdc4f155-6a1f-430b-8e30-3276091726e9" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_fnlc_MunicipalPortfolioSegmentMember_4b560ac1-2eb5-4524-ae05-eec5128f8e8a" xlink:href="fnlc-20260331.xsd#fnlc_MunicipalPortfolioSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_b353f852-b2c8-482e-9549-2cf9ba28f3e4" xlink:to="loc_fnlc_MunicipalPortfolioSegmentMember_4b560ac1-2eb5-4524-ae05-eec5128f8e8a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ResidentialPortfolioSegmentMember_c294963a-d506-4285-93da-723f462d7af7" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ResidentialPortfolioSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_b353f852-b2c8-482e-9549-2cf9ba28f3e4" xlink:to="loc_us-gaap_ResidentialPortfolioSegmentMember_c294963a-d506-4285-93da-723f462d7af7" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_fnlc_HomeEquityLineOfCreditPortfolioMember_1b314b6c-e461-4eb2-9ece-23659faa2558" xlink:href="fnlc-20260331.xsd#fnlc_HomeEquityLineOfCreditPortfolioMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_b353f852-b2c8-482e-9549-2cf9ba28f3e4" xlink:to="loc_fnlc_HomeEquityLineOfCreditPortfolioMember_1b314b6c-e461-4eb2-9ece-23659faa2558" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConsumerPortfolioSegmentMember_77dbbbf2-0840-4f6c-8327-9cfb3eaf471c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ConsumerPortfolioSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_b353f852-b2c8-482e-9549-2cf9ba28f3e4" xlink:to="loc_us-gaap_ConsumerPortfolioSegmentMember_77dbbbf2-0840-4f6c-8327-9cfb3eaf471c" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis_7ddc1417-8fa9-40fd-a977-c00383a934f9" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfAccountsNotesLoansAndFinancingReceivableTable_ec120f49-b6e4-4a79-8adf-37831256e5a6" xlink:to="loc_us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis_7ddc1417-8fa9-40fd-a977-c00383a934f9" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_7ddc1417-8fa9-40fd-a977-c00383a934f9_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis_7ddc1417-8fa9-40fd-a977-c00383a934f9" xlink:to="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_7ddc1417-8fa9-40fd-a977-c00383a934f9_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_4080356a-c72f-4f9f-8f8c-a9d38b3462ac" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis_7ddc1417-8fa9-40fd-a977-c00383a934f9" xlink:to="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_4080356a-c72f-4f9f-8f8c-a9d38b3462ac" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_fnlc_RealEstateLoanOwnerOccupiedMember_46792e18-cf93-4df5-903e-b26b58bb4e2f" xlink:href="fnlc-20260331.xsd#fnlc_RealEstateLoanOwnerOccupiedMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_4080356a-c72f-4f9f-8f8c-a9d38b3462ac" xlink:to="loc_fnlc_RealEstateLoanOwnerOccupiedMember_46792e18-cf93-4df5-903e-b26b58bb4e2f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_fnlc_RealEstateLoanNonOwnerOccupiedMember_07554e7d-6f6b-4b47-8d70-ae6df2b48424" xlink:href="fnlc-20260331.xsd#fnlc_RealEstateLoanNonOwnerOccupiedMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_4080356a-c72f-4f9f-8f8c-a9d38b3462ac" xlink:to="loc_fnlc_RealEstateLoanNonOwnerOccupiedMember_07554e7d-6f6b-4b47-8d70-ae6df2b48424" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConstructionLoansMember_13caa224-ac62-466d-ac84-c744f07a48e2" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ConstructionLoansMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_4080356a-c72f-4f9f-8f8c-a9d38b3462ac" xlink:to="loc_us-gaap_ConstructionLoansMember_13caa224-ac62-466d-ac84-c744f07a48e2" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_fnlc_CommercialAndIndustrialLoansMember_e2969916-43ea-4136-abb0-6fea01e46bd2" xlink:href="fnlc-20260331.xsd#fnlc_CommercialAndIndustrialLoansMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_4080356a-c72f-4f9f-8f8c-a9d38b3462ac" xlink:to="loc_fnlc_CommercialAndIndustrialLoansMember_e2969916-43ea-4136-abb0-6fea01e46bd2" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MultifamilyMember_687fc34d-12fa-45df-9731-2052bc5cea96" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_MultifamilyMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_4080356a-c72f-4f9f-8f8c-a9d38b3462ac" xlink:to="loc_srt_MultifamilyMember_687fc34d-12fa-45df-9731-2052bc5cea96" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_fnlc_AgricultureLoanMember_5d57e424-fc27-4a26-b9d0-63f221a56b62" xlink:href="fnlc-20260331.xsd#fnlc_AgricultureLoanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_4080356a-c72f-4f9f-8f8c-a9d38b3462ac" xlink:to="loc_fnlc_AgricultureLoanMember_5d57e424-fc27-4a26-b9d0-63f221a56b62" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_fnlc_TermLoanMember_3f956ed8-3d0e-4fec-a333-dd1569cd5dfc" xlink:href="fnlc-20260331.xsd#fnlc_TermLoanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_4080356a-c72f-4f9f-8f8c-a9d38b3462ac" xlink:to="loc_fnlc_TermLoanMember_3f956ed8-3d0e-4fec-a333-dd1569cd5dfc" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableExcludingAccruedInterestBeforeAllowanceForCreditLoss_ab7e8481-7ea2-43ea-a28b-23817f4dfddb" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FinancingReceivableExcludingAccruedInterestBeforeAllowanceForCreditLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AccountsNotesAndLoansReceivableLineItems_df963865-7ba1-4d98-8cf8-9b59bf7da4f5" xlink:to="loc_us-gaap_FinancingReceivableExcludingAccruedInterestBeforeAllowanceForCreditLoss_ab7e8481-7ea2-43ea-a28b-23817f4dfddb" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_fnlc_PercentageOfFinancingReceivableByType_48b1401d-7581-4d54-ae8e-1e9557755a04" xlink:href="fnlc-20260331.xsd#fnlc_PercentageOfFinancingReceivableByType"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AccountsNotesAndLoansReceivableLineItems_df963865-7ba1-4d98-8cf8-9b59bf7da4f5" xlink:to="loc_fnlc_PercentageOfFinancingReceivableByType_48b1401d-7581-4d54-ae8e-1e9557755a04" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.thefirst.com/role/LoansNarrativeDetails" xlink:type="simple" xlink:href="fnlc-20260331.xsd#LoansNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.thefirst.com/role/LoansNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccountsNotesAndLoansReceivableLineItems_bc6cc684-7cf8-44a6-99b9-30cf86460c2d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AccountsNotesAndLoansReceivableLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfAccountsNotesLoansAndFinancingReceivableTable_2839446a-5878-42b6-bf22-9de521d81eaa" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfAccountsNotesLoansAndFinancingReceivableTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_AccountsNotesAndLoansReceivableLineItems_bc6cc684-7cf8-44a6-99b9-30cf86460c2d" xlink:to="loc_us-gaap_ScheduleOfAccountsNotesLoansAndFinancingReceivableTable_2839446a-5878-42b6-bf22-9de521d81eaa" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentRiskAxis_019d2934-2cbe-792c-83fa-3e189258e92a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeInstrumentRiskAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfAccountsNotesLoansAndFinancingReceivableTable_2839446a-5878-42b6-bf22-9de521d81eaa" xlink:to="loc_us-gaap_DerivativeInstrumentRiskAxis_019d2934-2cbe-792c-83fa-3e189258e92a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_019d2934-2cbe-792c-83fa-3e189258e92a_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_019d2934-2cbe-792c-83fa-3e189258e92a" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_019d2934-2cbe-792c-83fa-3e189258e92a_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_019d2934-2cbe-7272-a282-9e5a1e3dcfed" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_019d2934-2cbe-792c-83fa-3e189258e92a" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_019d2934-2cbe-7272-a282-9e5a1e3dcfed" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestRateSwapMember_019d2934-2cbe-7679-afb3-442416ef778f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_InterestRateSwapMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_019d2934-2cbe-7272-a282-9e5a1e3dcfed" xlink:to="loc_us-gaap_InterestRateSwapMember_019d2934-2cbe-7679-afb3-442416ef778f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestRateCapMember_019d2934-5639-726e-877c-29006d40a129" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_InterestRateCapMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_019d2934-2cbe-7272-a282-9e5a1e3dcfed" xlink:to="loc_us-gaap_InterestRateCapMember_019d2934-5639-726e-877c-29006d40a129" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis_019d2934-2cbe-7a63-837e-ee6ad30ac44d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfAccountsNotesLoansAndFinancingReceivableTable_2839446a-5878-42b6-bf22-9de521d81eaa" xlink:to="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis_019d2934-2cbe-7a63-837e-ee6ad30ac44d" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingRelationshipDomain_019d2934-2cbe-7a63-837e-ee6ad30ac44d_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_HedgingRelationshipDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis_019d2934-2cbe-7a63-837e-ee6ad30ac44d" xlink:to="loc_us-gaap_HedgingRelationshipDomain_019d2934-2cbe-7a63-837e-ee6ad30ac44d_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingRelationshipDomain_019d2934-2cbe-75d6-8937-fd779bd207b4" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_HedgingRelationshipDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis_019d2934-2cbe-7a63-837e-ee6ad30ac44d" xlink:to="loc_us-gaap_HedgingRelationshipDomain_019d2934-2cbe-75d6-8937-fd779bd207b4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueHedgingMember_019d2934-2cbe-7873-888b-089c1eaf3994" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueHedgingMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_HedgingRelationshipDomain_019d2934-2cbe-75d6-8937-fd779bd207b4" xlink:to="loc_us-gaap_FairValueHedgingMember_019d2934-2cbe-7873-888b-089c1eaf3994" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingDesignationAxis_019d2934-2cbe-75a9-9c0e-d65cccd7b41e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_HedgingDesignationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfAccountsNotesLoansAndFinancingReceivableTable_2839446a-5878-42b6-bf22-9de521d81eaa" xlink:to="loc_us-gaap_HedgingDesignationAxis_019d2934-2cbe-75a9-9c0e-d65cccd7b41e" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingDesignationDomain_019d2934-2cbe-75a9-9c0e-d65cccd7b41e_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_HedgingDesignationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_HedgingDesignationAxis_019d2934-2cbe-75a9-9c0e-d65cccd7b41e" xlink:to="loc_us-gaap_HedgingDesignationDomain_019d2934-2cbe-75a9-9c0e-d65cccd7b41e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingDesignationDomain_019d2934-2cbe-7cf6-9fd8-ba6f10f6670e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_HedgingDesignationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_HedgingDesignationAxis_019d2934-2cbe-75a9-9c0e-d65cccd7b41e" xlink:to="loc_us-gaap_HedgingDesignationDomain_019d2934-2cbe-7cf6-9fd8-ba6f10f6670e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DesignatedAsHedgingInstrumentMember_019d2934-2cbe-7982-899e-46a8c74848d9" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DesignatedAsHedgingInstrumentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_HedgingDesignationDomain_019d2934-2cbe-7cf6-9fd8-ba6f10f6670e" xlink:to="loc_us-gaap_DesignatedAsHedgingInstrumentMember_019d2934-2cbe-7982-899e-46a8c74848d9" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivablePortfolioSegmentAxis_019d2934-5639-74f4-a74d-a205cb808fda" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FinancingReceivablePortfolioSegmentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfAccountsNotesLoansAndFinancingReceivableTable_2839446a-5878-42b6-bf22-9de521d81eaa" xlink:to="loc_us-gaap_FinancingReceivablePortfolioSegmentAxis_019d2934-5639-74f4-a74d-a205cb808fda" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_019d2934-5639-74f4-a74d-a205cb808fda_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FinancingReceivablePortfolioSegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FinancingReceivablePortfolioSegmentAxis_019d2934-5639-74f4-a74d-a205cb808fda" xlink:to="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_019d2934-5639-74f4-a74d-a205cb808fda_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_019d2934-5639-72e2-bed5-8c1949329212" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FinancingReceivablePortfolioSegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FinancingReceivablePortfolioSegmentAxis_019d2934-5639-74f4-a74d-a205cb808fda" xlink:to="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_019d2934-5639-72e2-bed5-8c1949329212" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ResidentialPortfolioSegmentMember_019d2934-5639-7b5f-941d-f1c8cf737d49" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ResidentialPortfolioSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_019d2934-5639-72e2-bed5-8c1949329212" xlink:to="loc_us-gaap_ResidentialPortfolioSegmentMember_019d2934-5639-7b5f-941d-f1c8cf737d49" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis_019d2934-5639-7ea6-8aa7-0268285b25e6" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfAccountsNotesLoansAndFinancingReceivableTable_2839446a-5878-42b6-bf22-9de521d81eaa" xlink:to="loc_us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis_019d2934-5639-7ea6-8aa7-0268285b25e6" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_019d2934-5639-7ea6-8aa7-0268285b25e6_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis_019d2934-5639-7ea6-8aa7-0268285b25e6" xlink:to="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_019d2934-5639-7ea6-8aa7-0268285b25e6_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_019d2934-5639-75e2-972d-dff85d0e3d68" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis_019d2934-5639-7ea6-8aa7-0268285b25e6" xlink:to="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_019d2934-5639-75e2-972d-dff85d0e3d68" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_fnlc_TermLoanMember_019d2934-5639-7d19-a140-9da457783740" xlink:href="fnlc-20260331.xsd#fnlc_TermLoanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_019d2934-5639-75e2-972d-dff85d0e3d68" xlink:to="loc_fnlc_TermLoanMember_019d2934-5639-7d19-a140-9da457783740" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PledgedStatusAxis_019d2934-5639-7e9e-a315-723b7c560c74" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PledgedStatusAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfAccountsNotesLoansAndFinancingReceivableTable_2839446a-5878-42b6-bf22-9de521d81eaa" xlink:to="loc_us-gaap_PledgedStatusAxis_019d2934-5639-7e9e-a315-723b7c560c74" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PledgedStatusDomain_019d2934-5639-7e9e-a315-723b7c560c74_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PledgedStatusDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PledgedStatusAxis_019d2934-5639-7e9e-a315-723b7c560c74" xlink:to="loc_us-gaap_PledgedStatusDomain_019d2934-5639-7e9e-a315-723b7c560c74_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PledgedStatusDomain_019d2934-5639-7d3a-86be-dd8705fe0c46" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PledgedStatusDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PledgedStatusAxis_019d2934-5639-7e9e-a315-723b7c560c74" xlink:to="loc_us-gaap_PledgedStatusDomain_019d2934-5639-7d3a-86be-dd8705fe0c46" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetPledgedAsCollateralMember_019d2934-5639-75fd-a497-cd9a50ad527a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AssetPledgedAsCollateralMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PledgedStatusDomain_019d2934-5639-7d3a-86be-dd8705fe0c46" xlink:to="loc_us-gaap_AssetPledgedAsCollateralMember_019d2934-5639-75fd-a497-cd9a50ad527a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancialInstrumentAxis_019d2934-db6e-790a-bb55-23a2380bf90e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FinancialInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfAccountsNotesLoansAndFinancingReceivableTable_2839446a-5878-42b6-bf22-9de521d81eaa" xlink:to="loc_us-gaap_FinancialInstrumentAxis_019d2934-db6e-790a-bb55-23a2380bf90e" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019d2934-db6e-790a-bb55-23a2380bf90e_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FinancialInstrumentAxis_019d2934-db6e-790a-bb55-23a2380bf90e" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019d2934-db6e-790a-bb55-23a2380bf90e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019d2934-db6e-7123-b1c5-6ee74212ed0e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FinancialInstrumentAxis_019d2934-db6e-790a-bb55-23a2380bf90e" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019d2934-db6e-7123-b1c5-6ee74212ed0e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HomeEquityMember_019d2934-db6e-7e7f-8ebd-e8cf4824145b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_HomeEquityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019d2934-db6e-7123-b1c5-6ee74212ed0e" xlink:to="loc_us-gaap_HomeEquityMember_019d2934-db6e-7e7f-8ebd-e8cf4824145b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConsumerLoanMember_019d2934-db6e-7930-b66d-490832c3a482" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ConsumerLoanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019d2934-db6e-7123-b1c5-6ee74212ed0e" xlink:to="loc_us-gaap_ConsumerLoanMember_019d2934-db6e-7930-b66d-490832c3a482" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommercialLoanMember_019d2934-db6e-751f-afb6-acccdd58d0b6" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CommercialLoanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019d2934-db6e-7123-b1c5-6ee74212ed0e" xlink:to="loc_us-gaap_CommercialLoanMember_019d2934-db6e-751f-afb6-acccdd58d0b6" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableDeferredIncome_019d2934-2cbe-747d-9149-83020787f466" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FinancingReceivableDeferredIncome"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AccountsNotesAndLoansReceivableLineItems_bc6cc684-7cf8-44a6-99b9-30cf86460c2d" xlink:to="loc_us-gaap_FinancingReceivableDeferredIncome_019d2934-2cbe-747d-9149-83020787f466" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeFairValueOfDerivativeNet_019d2934-2cbe-7f2a-bbc3-c9cd30416a60" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeFairValueOfDerivativeNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AccountsNotesAndLoansReceivableLineItems_bc6cc684-7cf8-44a6-99b9-30cf86460c2d" xlink:to="loc_us-gaap_DerivativeFairValueOfDerivativeNet_019d2934-2cbe-7f2a-bbc3-c9cd30416a60" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FederalHomeLoanBankAdvancesGeneralDebtObligationsDisclosuresCollateralPledged1_019d2934-5639-7610-991f-a84a082c1445" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FederalHomeLoanBankAdvancesGeneralDebtObligationsDisclosuresCollateralPledged1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AccountsNotesAndLoansReceivableLineItems_bc6cc684-7cf8-44a6-99b9-30cf86460c2d" xlink:to="loc_us-gaap_FederalHomeLoanBankAdvancesGeneralDebtObligationsDisclosuresCollateralPledged1_019d2934-5639-7610-991f-a84a082c1445" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableExcludingAccruedInterestBeforeAllowanceForCreditLoss_019d2934-5639-7790-91a2-0f56adcc1783" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FinancingReceivableExcludingAccruedInterestBeforeAllowanceForCreditLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AccountsNotesAndLoansReceivableLineItems_bc6cc684-7cf8-44a6-99b9-30cf86460c2d" xlink:to="loc_us-gaap_FinancingReceivableExcludingAccruedInterestBeforeAllowanceForCreditLoss_019d2934-5639-7790-91a2-0f56adcc1783" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_fnlc_MortgageLoansinProcessofForeclosureNumber_019d2934-db6e-7c6e-830f-ac850d9a9800" xlink:href="fnlc-20260331.xsd#fnlc_MortgageLoansinProcessofForeclosureNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AccountsNotesAndLoansReceivableLineItems_bc6cc684-7cf8-44a6-99b9-30cf86460c2d" xlink:to="loc_fnlc_MortgageLoansinProcessofForeclosureNumber_019d2934-db6e-7c6e-830f-ac850d9a9800" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MortgageLoansInProcessOfForeclosureAmount_019d2934-db6e-7496-9221-89866d96be70" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_MortgageLoansInProcessOfForeclosureAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AccountsNotesAndLoansReceivableLineItems_bc6cc684-7cf8-44a6-99b9-30cf86460c2d" xlink:to="loc_us-gaap_MortgageLoansInProcessOfForeclosureAmount_019d2934-db6e-7496-9221-89866d96be70" xlink:type="arc" order="5"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.thefirst.com/role/LoansPastdueStatusofLoansbyClassDetails" xlink:type="simple" xlink:href="fnlc-20260331.xsd#LoansPastdueStatusofLoansbyClassDetails"/>
  <link:definitionLink xlink:role="http://www.thefirst.com/role/LoansPastdueStatusofLoansbyClassDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableRecordedInvestmentPastDueLineItems_7256c4e7-b180-432e-90d5-e10ca4029aaa" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FinancingReceivableRecordedInvestmentPastDueLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfFinancingReceivablesPastDueTable_ee8cae7e-7d25-48b4-965b-3a14fc9c7cb1" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfFinancingReceivablesPastDueTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentPastDueLineItems_7256c4e7-b180-432e-90d5-e10ca4029aaa" xlink:to="loc_us-gaap_ScheduleOfFinancingReceivablesPastDueTable_ee8cae7e-7d25-48b4-965b-3a14fc9c7cb1" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivablePortfolioSegmentAxis_c0365d23-5aa5-4d57-aa4a-628b6bbf4d3a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FinancingReceivablePortfolioSegmentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfFinancingReceivablesPastDueTable_ee8cae7e-7d25-48b4-965b-3a14fc9c7cb1" xlink:to="loc_us-gaap_FinancingReceivablePortfolioSegmentAxis_c0365d23-5aa5-4d57-aa4a-628b6bbf4d3a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_c0365d23-5aa5-4d57-aa4a-628b6bbf4d3a_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FinancingReceivablePortfolioSegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FinancingReceivablePortfolioSegmentAxis_c0365d23-5aa5-4d57-aa4a-628b6bbf4d3a" xlink:to="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_c0365d23-5aa5-4d57-aa4a-628b6bbf4d3a_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_9e7e4d3a-068d-4045-9d33-8d68c2942b23" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FinancingReceivablePortfolioSegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FinancingReceivablePortfolioSegmentAxis_c0365d23-5aa5-4d57-aa4a-628b6bbf4d3a" xlink:to="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_9e7e4d3a-068d-4045-9d33-8d68c2942b23" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommercialPortfolioSegmentMember_b210d5e1-292f-4e55-b3ce-e346f76699ff" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CommercialPortfolioSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_9e7e4d3a-068d-4045-9d33-8d68c2942b23" xlink:to="loc_us-gaap_CommercialPortfolioSegmentMember_b210d5e1-292f-4e55-b3ce-e346f76699ff" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_fnlc_MunicipalPortfolioSegmentMember_9a521830-fea6-404e-846c-9c62c6b8ba9f" xlink:href="fnlc-20260331.xsd#fnlc_MunicipalPortfolioSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_9e7e4d3a-068d-4045-9d33-8d68c2942b23" xlink:to="loc_fnlc_MunicipalPortfolioSegmentMember_9a521830-fea6-404e-846c-9c62c6b8ba9f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ResidentialPortfolioSegmentMember_ac3cf018-829f-41c6-bb28-97bbcd91f9cb" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ResidentialPortfolioSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_9e7e4d3a-068d-4045-9d33-8d68c2942b23" xlink:to="loc_us-gaap_ResidentialPortfolioSegmentMember_ac3cf018-829f-41c6-bb28-97bbcd91f9cb" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_fnlc_HomeEquityLineOfCreditPortfolioMember_5bfdc100-57c5-4322-9b60-94002ba82f1a" xlink:href="fnlc-20260331.xsd#fnlc_HomeEquityLineOfCreditPortfolioMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_9e7e4d3a-068d-4045-9d33-8d68c2942b23" xlink:to="loc_fnlc_HomeEquityLineOfCreditPortfolioMember_5bfdc100-57c5-4322-9b60-94002ba82f1a" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConsumerPortfolioSegmentMember_3518f57b-ef83-44ba-88f8-d64652554778" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ConsumerPortfolioSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_9e7e4d3a-068d-4045-9d33-8d68c2942b23" xlink:to="loc_us-gaap_ConsumerPortfolioSegmentMember_3518f57b-ef83-44ba-88f8-d64652554778" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis_06a77873-f342-43f8-9c1f-5ac1fac6ea7d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfFinancingReceivablesPastDueTable_ee8cae7e-7d25-48b4-965b-3a14fc9c7cb1" xlink:to="loc_us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis_06a77873-f342-43f8-9c1f-5ac1fac6ea7d" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_06a77873-f342-43f8-9c1f-5ac1fac6ea7d_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis_06a77873-f342-43f8-9c1f-5ac1fac6ea7d" xlink:to="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_06a77873-f342-43f8-9c1f-5ac1fac6ea7d_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_a81975be-c5da-4343-b16b-6a62afee6e63" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis_06a77873-f342-43f8-9c1f-5ac1fac6ea7d" xlink:to="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_a81975be-c5da-4343-b16b-6a62afee6e63" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_fnlc_RealEstateLoanOwnerOccupiedMember_736f98de-0052-495b-9e93-799a4a05e8da" xlink:href="fnlc-20260331.xsd#fnlc_RealEstateLoanOwnerOccupiedMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_a81975be-c5da-4343-b16b-6a62afee6e63" xlink:to="loc_fnlc_RealEstateLoanOwnerOccupiedMember_736f98de-0052-495b-9e93-799a4a05e8da" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_fnlc_RealEstateLoanNonOwnerOccupiedMember_9282f9b1-0497-400a-a9e4-d73e99517abb" xlink:href="fnlc-20260331.xsd#fnlc_RealEstateLoanNonOwnerOccupiedMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_a81975be-c5da-4343-b16b-6a62afee6e63" xlink:to="loc_fnlc_RealEstateLoanNonOwnerOccupiedMember_9282f9b1-0497-400a-a9e4-d73e99517abb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConstructionLoansMember_423c2623-d99e-480e-86fb-092e0656651d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ConstructionLoansMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_a81975be-c5da-4343-b16b-6a62afee6e63" xlink:to="loc_us-gaap_ConstructionLoansMember_423c2623-d99e-480e-86fb-092e0656651d" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_fnlc_CommercialAndIndustrialLoansMember_f119c251-45ba-45e8-82b2-f1bcb705bdfa" xlink:href="fnlc-20260331.xsd#fnlc_CommercialAndIndustrialLoansMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_a81975be-c5da-4343-b16b-6a62afee6e63" xlink:to="loc_fnlc_CommercialAndIndustrialLoansMember_f119c251-45ba-45e8-82b2-f1bcb705bdfa" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MultifamilyMember_96047be4-6a26-4ad3-b495-ba701bd12bd6" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_MultifamilyMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_a81975be-c5da-4343-b16b-6a62afee6e63" xlink:to="loc_srt_MultifamilyMember_96047be4-6a26-4ad3-b495-ba701bd12bd6" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_fnlc_AgricultureLoanMember_fdec63b3-78ea-41fa-8696-1650162b0ca9" xlink:href="fnlc-20260331.xsd#fnlc_AgricultureLoanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_a81975be-c5da-4343-b16b-6a62afee6e63" xlink:to="loc_fnlc_AgricultureLoanMember_fdec63b3-78ea-41fa-8696-1650162b0ca9" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_fnlc_TermLoanMember_d2d95bd0-2fca-4726-bc98-0b7c69a682fd" xlink:href="fnlc-20260331.xsd#fnlc_TermLoanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_a81975be-c5da-4343-b16b-6a62afee6e63" xlink:to="loc_fnlc_TermLoanMember_d2d95bd0-2fca-4726-bc98-0b7c69a682fd" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivablesPeriodPastDueAxis_9f8c5397-091d-45fe-b3d5-f00016ffa3e0" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FinancingReceivablesPeriodPastDueAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfFinancingReceivablesPastDueTable_ee8cae7e-7d25-48b4-965b-3a14fc9c7cb1" xlink:to="loc_us-gaap_FinancingReceivablesPeriodPastDueAxis_9f8c5397-091d-45fe-b3d5-f00016ffa3e0" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivablesPeriodPastDueDomain_9f8c5397-091d-45fe-b3d5-f00016ffa3e0_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FinancingReceivablesPeriodPastDueDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FinancingReceivablesPeriodPastDueAxis_9f8c5397-091d-45fe-b3d5-f00016ffa3e0" xlink:to="loc_us-gaap_FinancingReceivablesPeriodPastDueDomain_9f8c5397-091d-45fe-b3d5-f00016ffa3e0_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivablesPeriodPastDueDomain_cc91957f-ac77-4768-9238-86f4f481a176" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FinancingReceivablesPeriodPastDueDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FinancingReceivablesPeriodPastDueAxis_9f8c5397-091d-45fe-b3d5-f00016ffa3e0" xlink:to="loc_us-gaap_FinancingReceivablesPeriodPastDueDomain_cc91957f-ac77-4768-9238-86f4f481a176" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivables30To59DaysPastDueMember_78690884-0a70-4c81-82a0-9a29d0c096d3" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FinancingReceivables30To59DaysPastDueMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivablesPeriodPastDueDomain_cc91957f-ac77-4768-9238-86f4f481a176" xlink:to="loc_us-gaap_FinancingReceivables30To59DaysPastDueMember_78690884-0a70-4c81-82a0-9a29d0c096d3" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivables60To89DaysPastDueMember_8c427f62-4a4d-4779-a905-23ff4500ffac" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FinancingReceivables60To89DaysPastDueMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivablesPeriodPastDueDomain_cc91957f-ac77-4768-9238-86f4f481a176" xlink:to="loc_us-gaap_FinancingReceivables60To89DaysPastDueMember_8c427f62-4a4d-4779-a905-23ff4500ffac" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivablesEqualToGreaterThan90DaysPastDueMember_5f5aa1d4-4bbc-43d4-8d2c-0ece6355a25a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FinancingReceivablesEqualToGreaterThan90DaysPastDueMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivablesPeriodPastDueDomain_cc91957f-ac77-4768-9238-86f4f481a176" xlink:to="loc_us-gaap_FinancingReceivablesEqualToGreaterThan90DaysPastDueMember_5f5aa1d4-4bbc-43d4-8d2c-0ece6355a25a" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancialAssetPastDueMember_8d98b24a-95f2-452b-89b3-ae2fb859131f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FinancialAssetPastDueMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivablesPeriodPastDueDomain_cc91957f-ac77-4768-9238-86f4f481a176" xlink:to="loc_us-gaap_FinancialAssetPastDueMember_8d98b24a-95f2-452b-89b3-ae2fb859131f" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancialAssetNotPastDueMember_9fa7223c-62f2-4607-83e5-3d0c05ac6e50" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FinancialAssetNotPastDueMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivablesPeriodPastDueDomain_cc91957f-ac77-4768-9238-86f4f481a176" xlink:to="loc_us-gaap_FinancialAssetNotPastDueMember_9fa7223c-62f2-4607-83e5-3d0c05ac6e50" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableExcludingAccruedInterestBeforeAllowanceForCreditLoss_2920bae0-0d9c-4d26-bb89-5ebec3cbf4ac" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FinancingReceivableExcludingAccruedInterestBeforeAllowanceForCreditLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentPastDueLineItems_7256c4e7-b180-432e-90d5-e10ca4029aaa" xlink:to="loc_us-gaap_FinancingReceivableExcludingAccruedInterestBeforeAllowanceForCreditLoss_2920bae0-0d9c-4d26-bb89-5ebec3cbf4ac" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableRecordedInvestment90DaysPastDueAndStillAccruing_dbf6f9f7-5015-4caf-863b-65e68e12fb27" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FinancingReceivableRecordedInvestment90DaysPastDueAndStillAccruing"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentPastDueLineItems_7256c4e7-b180-432e-90d5-e10ca4029aaa" xlink:to="loc_us-gaap_FinancingReceivableRecordedInvestment90DaysPastDueAndStillAccruing_dbf6f9f7-5015-4caf-863b-65e68e12fb27" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.thefirst.com/role/LoansNonaccrualLoansDetails" xlink:type="simple" xlink:href="fnlc-20260331.xsd#LoansNonaccrualLoansDetails"/>
  <link:definitionLink xlink:role="http://www.thefirst.com/role/LoansNonaccrualLoansDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableNonaccrualStatusLineItems_cde62771-d406-463c-a049-b66114af62d1" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FinancingReceivableNonaccrualStatusLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableNonaccrualTable_f16b34d6-b2b4-4c18-802f-e0d342d215c2" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FinancingReceivableNonaccrualTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FinancingReceivableNonaccrualStatusLineItems_cde62771-d406-463c-a049-b66114af62d1" xlink:to="loc_us-gaap_FinancingReceivableNonaccrualTable_f16b34d6-b2b4-4c18-802f-e0d342d215c2" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivablePortfolioSegmentAxis_151ec15b-2c17-4184-b351-de38bb2dead3" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FinancingReceivablePortfolioSegmentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FinancingReceivableNonaccrualTable_f16b34d6-b2b4-4c18-802f-e0d342d215c2" xlink:to="loc_us-gaap_FinancingReceivablePortfolioSegmentAxis_151ec15b-2c17-4184-b351-de38bb2dead3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_151ec15b-2c17-4184-b351-de38bb2dead3_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FinancingReceivablePortfolioSegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FinancingReceivablePortfolioSegmentAxis_151ec15b-2c17-4184-b351-de38bb2dead3" xlink:to="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_151ec15b-2c17-4184-b351-de38bb2dead3_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_09840c72-0c1e-4e20-ac6b-c41a0f83a636" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FinancingReceivablePortfolioSegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FinancingReceivablePortfolioSegmentAxis_151ec15b-2c17-4184-b351-de38bb2dead3" xlink:to="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_09840c72-0c1e-4e20-ac6b-c41a0f83a636" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommercialPortfolioSegmentMember_e86c7d26-5c1e-4d4d-821c-672bce694697" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CommercialPortfolioSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_09840c72-0c1e-4e20-ac6b-c41a0f83a636" xlink:to="loc_us-gaap_CommercialPortfolioSegmentMember_e86c7d26-5c1e-4d4d-821c-672bce694697" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_fnlc_MunicipalPortfolioSegmentMember_9ac231c8-b785-48f9-895b-14471ef910d1" xlink:href="fnlc-20260331.xsd#fnlc_MunicipalPortfolioSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_09840c72-0c1e-4e20-ac6b-c41a0f83a636" xlink:to="loc_fnlc_MunicipalPortfolioSegmentMember_9ac231c8-b785-48f9-895b-14471ef910d1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ResidentialPortfolioSegmentMember_b79414bd-7c5f-4087-a879-3c8a9dd840e3" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ResidentialPortfolioSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_09840c72-0c1e-4e20-ac6b-c41a0f83a636" xlink:to="loc_us-gaap_ResidentialPortfolioSegmentMember_b79414bd-7c5f-4087-a879-3c8a9dd840e3" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_fnlc_HomeEquityLineOfCreditPortfolioMember_85f14d02-8262-4b8f-8581-772efa955280" xlink:href="fnlc-20260331.xsd#fnlc_HomeEquityLineOfCreditPortfolioMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_09840c72-0c1e-4e20-ac6b-c41a0f83a636" xlink:to="loc_fnlc_HomeEquityLineOfCreditPortfolioMember_85f14d02-8262-4b8f-8581-772efa955280" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConsumerPortfolioSegmentMember_42fad4d7-7578-4aad-a4ff-b40c5d2ec665" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ConsumerPortfolioSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_09840c72-0c1e-4e20-ac6b-c41a0f83a636" xlink:to="loc_us-gaap_ConsumerPortfolioSegmentMember_42fad4d7-7578-4aad-a4ff-b40c5d2ec665" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis_22bd8881-9f19-4cb7-992c-f0cf86eeee27" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FinancingReceivableNonaccrualTable_f16b34d6-b2b4-4c18-802f-e0d342d215c2" xlink:to="loc_us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis_22bd8881-9f19-4cb7-992c-f0cf86eeee27" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_22bd8881-9f19-4cb7-992c-f0cf86eeee27_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis_22bd8881-9f19-4cb7-992c-f0cf86eeee27" xlink:to="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_22bd8881-9f19-4cb7-992c-f0cf86eeee27_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_46f449da-b860-42ff-a318-7fcd58d12daa" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis_22bd8881-9f19-4cb7-992c-f0cf86eeee27" xlink:to="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_46f449da-b860-42ff-a318-7fcd58d12daa" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_fnlc_RealEstateLoanOwnerOccupiedMember_8e9c1153-44de-414a-a673-3bd82891decf" xlink:href="fnlc-20260331.xsd#fnlc_RealEstateLoanOwnerOccupiedMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_46f449da-b860-42ff-a318-7fcd58d12daa" xlink:to="loc_fnlc_RealEstateLoanOwnerOccupiedMember_8e9c1153-44de-414a-a673-3bd82891decf" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_fnlc_RealEstateLoanNonOwnerOccupiedMember_fd575d67-16c0-4424-9865-5de68240e167" xlink:href="fnlc-20260331.xsd#fnlc_RealEstateLoanNonOwnerOccupiedMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_46f449da-b860-42ff-a318-7fcd58d12daa" xlink:to="loc_fnlc_RealEstateLoanNonOwnerOccupiedMember_fd575d67-16c0-4424-9865-5de68240e167" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConstructionLoansMember_7b74d3bd-587c-4a3a-8921-9486bcd7bfda" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ConstructionLoansMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_46f449da-b860-42ff-a318-7fcd58d12daa" xlink:to="loc_us-gaap_ConstructionLoansMember_7b74d3bd-587c-4a3a-8921-9486bcd7bfda" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_fnlc_CommercialAndIndustrialLoansMember_216e9782-49ce-49e6-afe4-472d5fa6954e" xlink:href="fnlc-20260331.xsd#fnlc_CommercialAndIndustrialLoansMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_46f449da-b860-42ff-a318-7fcd58d12daa" xlink:to="loc_fnlc_CommercialAndIndustrialLoansMember_216e9782-49ce-49e6-afe4-472d5fa6954e" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MultifamilyMember_1829dad4-8fbe-4cca-9bea-8bdd488d9893" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_MultifamilyMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_46f449da-b860-42ff-a318-7fcd58d12daa" xlink:to="loc_srt_MultifamilyMember_1829dad4-8fbe-4cca-9bea-8bdd488d9893" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_fnlc_AgricultureLoanMember_b4807ab5-c817-400e-9235-b0b1d44e7cee" xlink:href="fnlc-20260331.xsd#fnlc_AgricultureLoanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_46f449da-b860-42ff-a318-7fcd58d12daa" xlink:to="loc_fnlc_AgricultureLoanMember_b4807ab5-c817-400e-9235-b0b1d44e7cee" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_fnlc_TermLoanMember_2cd68f52-d1b8-461e-b003-2a1b255f3bb8" xlink:href="fnlc-20260331.xsd#fnlc_TermLoanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_46f449da-b860-42ff-a318-7fcd58d12daa" xlink:to="loc_fnlc_TermLoanMember_2cd68f52-d1b8-461e-b003-2a1b255f3bb8" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_fnlc_FinancingReceivableNonaccrualWithAllowance_76dc7128-d999-46ab-bdb3-873d59ae02fe" xlink:href="fnlc-20260331.xsd#fnlc_FinancingReceivableNonaccrualWithAllowance"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableNonaccrualStatusLineItems_cde62771-d406-463c-a049-b66114af62d1" xlink:to="loc_fnlc_FinancingReceivableNonaccrualWithAllowance_76dc7128-d999-46ab-bdb3-873d59ae02fe" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableNonaccrualNoAllowance_b996ddf7-8161-4dd0-ae3e-b1da58b89495" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FinancingReceivableNonaccrualNoAllowance"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableNonaccrualStatusLineItems_cde62771-d406-463c-a049-b66114af62d1" xlink:to="loc_us-gaap_FinancingReceivableNonaccrualNoAllowance_b996ddf7-8161-4dd0-ae3e-b1da58b89495" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableRecordedInvestmentNonaccrualStatus_35dae428-dcd4-43fb-b547-9fe154521153" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FinancingReceivableRecordedInvestmentNonaccrualStatus"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableNonaccrualStatusLineItems_cde62771-d406-463c-a049-b66114af62d1" xlink:to="loc_us-gaap_FinancingReceivableRecordedInvestmentNonaccrualStatus_35dae428-dcd4-43fb-b547-9fe154521153" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.thefirst.com/role/LoansAmortizedCostBasisofCollateralDependentLoansDetails" xlink:type="simple" xlink:href="fnlc-20260331.xsd#LoansAmortizedCostBasisofCollateralDependentLoansDetails"/>
  <link:definitionLink xlink:role="http://www.thefirst.com/role/LoansAmortizedCostBasisofCollateralDependentLoansDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccountsNotesAndLoansReceivableLineItems_d5045e65-2a56-4607-88e1-1ceb5f54cad8" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AccountsNotesAndLoansReceivableLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfAccountsNotesLoansAndFinancingReceivableTable_7c3ef254-cfd2-49a2-ab60-5e5619c95f27" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfAccountsNotesLoansAndFinancingReceivableTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_AccountsNotesAndLoansReceivableLineItems_d5045e65-2a56-4607-88e1-1ceb5f54cad8" xlink:to="loc_us-gaap_ScheduleOfAccountsNotesLoansAndFinancingReceivableTable_7c3ef254-cfd2-49a2-ab60-5e5619c95f27" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CollateralAxis_a507febd-ae94-4b5e-ac14-cb6d1a1f84bb" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CollateralAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfAccountsNotesLoansAndFinancingReceivableTable_7c3ef254-cfd2-49a2-ab60-5e5619c95f27" xlink:to="loc_us-gaap_CollateralAxis_a507febd-ae94-4b5e-ac14-cb6d1a1f84bb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CollateralDomain_a507febd-ae94-4b5e-ac14-cb6d1a1f84bb_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CollateralDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_CollateralAxis_a507febd-ae94-4b5e-ac14-cb6d1a1f84bb" xlink:to="loc_us-gaap_CollateralDomain_a507febd-ae94-4b5e-ac14-cb6d1a1f84bb_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CollateralDomain_d5019e9d-0087-47cb-9aa0-dc0b729ac904" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CollateralDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_CollateralAxis_a507febd-ae94-4b5e-ac14-cb6d1a1f84bb" xlink:to="loc_us-gaap_CollateralDomain_d5019e9d-0087-47cb-9aa0-dc0b729ac904" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommercialRealEstateMember_f5c2983f-6f99-435b-b0bd-1392ecf67bad" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CommercialRealEstateMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CollateralDomain_d5019e9d-0087-47cb-9aa0-dc0b729ac904" xlink:to="loc_us-gaap_CommercialRealEstateMember_f5c2983f-6f99-435b-b0bd-1392ecf67bad" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ResidentialRealEstateMember_7dc45a1f-62c3-49ae-becc-4240d22e8f43" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ResidentialRealEstateMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CollateralDomain_d5019e9d-0087-47cb-9aa0-dc0b729ac904" xlink:to="loc_us-gaap_ResidentialRealEstateMember_7dc45a1f-62c3-49ae-becc-4240d22e8f43" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_fnlc_OtherCollateralMember_254ef65d-3716-4fd6-9edb-b3619def4d2c" xlink:href="fnlc-20260331.xsd#fnlc_OtherCollateralMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CollateralDomain_d5019e9d-0087-47cb-9aa0-dc0b729ac904" xlink:to="loc_fnlc_OtherCollateralMember_254ef65d-3716-4fd6-9edb-b3619def4d2c" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivablePortfolioSegmentAxis_0af1f607-b8d4-470d-9f0e-88788c156139" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FinancingReceivablePortfolioSegmentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfAccountsNotesLoansAndFinancingReceivableTable_7c3ef254-cfd2-49a2-ab60-5e5619c95f27" xlink:to="loc_us-gaap_FinancingReceivablePortfolioSegmentAxis_0af1f607-b8d4-470d-9f0e-88788c156139" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_0af1f607-b8d4-470d-9f0e-88788c156139_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FinancingReceivablePortfolioSegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FinancingReceivablePortfolioSegmentAxis_0af1f607-b8d4-470d-9f0e-88788c156139" xlink:to="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_0af1f607-b8d4-470d-9f0e-88788c156139_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_844da3c3-b3e7-45f7-b682-5f092841ef53" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FinancingReceivablePortfolioSegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FinancingReceivablePortfolioSegmentAxis_0af1f607-b8d4-470d-9f0e-88788c156139" xlink:to="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_844da3c3-b3e7-45f7-b682-5f092841ef53" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommercialPortfolioSegmentMember_c341a948-75f1-4942-989a-1a1f67b44f6b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CommercialPortfolioSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_844da3c3-b3e7-45f7-b682-5f092841ef53" xlink:to="loc_us-gaap_CommercialPortfolioSegmentMember_c341a948-75f1-4942-989a-1a1f67b44f6b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_fnlc_MunicipalPortfolioSegmentMember_d65e81f3-1739-4aa5-913d-6af86112716e" xlink:href="fnlc-20260331.xsd#fnlc_MunicipalPortfolioSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_844da3c3-b3e7-45f7-b682-5f092841ef53" xlink:to="loc_fnlc_MunicipalPortfolioSegmentMember_d65e81f3-1739-4aa5-913d-6af86112716e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ResidentialPortfolioSegmentMember_ac5397eb-6c6e-4fde-aab3-9770b4553477" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ResidentialPortfolioSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_844da3c3-b3e7-45f7-b682-5f092841ef53" xlink:to="loc_us-gaap_ResidentialPortfolioSegmentMember_ac5397eb-6c6e-4fde-aab3-9770b4553477" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_fnlc_HomeEquityLineOfCreditPortfolioMember_0926d0f2-9000-4b54-b58a-8d85c2a66ee3" xlink:href="fnlc-20260331.xsd#fnlc_HomeEquityLineOfCreditPortfolioMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_844da3c3-b3e7-45f7-b682-5f092841ef53" xlink:to="loc_fnlc_HomeEquityLineOfCreditPortfolioMember_0926d0f2-9000-4b54-b58a-8d85c2a66ee3" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConsumerPortfolioSegmentMember_faf26798-fd81-4b61-8adc-17107671129d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ConsumerPortfolioSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_844da3c3-b3e7-45f7-b682-5f092841ef53" xlink:to="loc_us-gaap_ConsumerPortfolioSegmentMember_faf26798-fd81-4b61-8adc-17107671129d" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis_a901c399-217d-4616-af21-35169f926a15" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfAccountsNotesLoansAndFinancingReceivableTable_7c3ef254-cfd2-49a2-ab60-5e5619c95f27" xlink:to="loc_us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis_a901c399-217d-4616-af21-35169f926a15" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_a901c399-217d-4616-af21-35169f926a15_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis_a901c399-217d-4616-af21-35169f926a15" xlink:to="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_a901c399-217d-4616-af21-35169f926a15_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_559802ae-39f9-4811-858d-52306c355411" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis_a901c399-217d-4616-af21-35169f926a15" xlink:to="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_559802ae-39f9-4811-858d-52306c355411" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_fnlc_RealEstateLoanOwnerOccupiedMember_6cbd9db3-4828-4080-82fa-6090c86084fc" xlink:href="fnlc-20260331.xsd#fnlc_RealEstateLoanOwnerOccupiedMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_559802ae-39f9-4811-858d-52306c355411" xlink:to="loc_fnlc_RealEstateLoanOwnerOccupiedMember_6cbd9db3-4828-4080-82fa-6090c86084fc" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_fnlc_RealEstateLoanNonOwnerOccupiedMember_e3b484f2-1b6f-4f07-9ff4-0b1d2f542ce8" xlink:href="fnlc-20260331.xsd#fnlc_RealEstateLoanNonOwnerOccupiedMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_559802ae-39f9-4811-858d-52306c355411" xlink:to="loc_fnlc_RealEstateLoanNonOwnerOccupiedMember_e3b484f2-1b6f-4f07-9ff4-0b1d2f542ce8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConstructionLoansMember_8779213f-2b1c-4b16-a939-eada3031e2b2" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ConstructionLoansMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_559802ae-39f9-4811-858d-52306c355411" xlink:to="loc_us-gaap_ConstructionLoansMember_8779213f-2b1c-4b16-a939-eada3031e2b2" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_fnlc_CommercialAndIndustrialLoansMember_840f5908-0014-4cb3-b98a-ffe1a3acba94" xlink:href="fnlc-20260331.xsd#fnlc_CommercialAndIndustrialLoansMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_559802ae-39f9-4811-858d-52306c355411" xlink:to="loc_fnlc_CommercialAndIndustrialLoansMember_840f5908-0014-4cb3-b98a-ffe1a3acba94" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MultifamilyMember_4a8c80e7-b1e9-4308-b2c8-6e41b65703e5" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_MultifamilyMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_559802ae-39f9-4811-858d-52306c355411" xlink:to="loc_srt_MultifamilyMember_4a8c80e7-b1e9-4308-b2c8-6e41b65703e5" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_fnlc_AgricultureLoanMember_e573a88e-024b-4413-8756-b677a63f6d2f" xlink:href="fnlc-20260331.xsd#fnlc_AgricultureLoanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_559802ae-39f9-4811-858d-52306c355411" xlink:to="loc_fnlc_AgricultureLoanMember_e573a88e-024b-4413-8756-b677a63f6d2f" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_fnlc_TermLoanMember_0326550b-9d82-4237-8673-32f8a63131c5" xlink:href="fnlc-20260331.xsd#fnlc_TermLoanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_559802ae-39f9-4811-858d-52306c355411" xlink:to="loc_fnlc_TermLoanMember_0326550b-9d82-4237-8673-32f8a63131c5" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment_4c4bebf7-8baf-4374-9546-a120bbe78f90" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AccountsNotesAndLoansReceivableLineItems_d5045e65-2a56-4607-88e1-1ceb5f54cad8" xlink:to="loc_us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment_4c4bebf7-8baf-4374-9546-a120bbe78f90" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.thefirst.com/role/LoansLoanModificationsDetails" xlink:type="simple" xlink:href="fnlc-20260331.xsd#LoansLoanModificationsDetails"/>
  <link:definitionLink xlink:role="http://www.thefirst.com/role/LoansLoanModificationsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableModificationsLineItems_4bbd8dfb-cf1e-48cd-a633-5fd8b6172ed5" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FinancingReceivableModificationsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfFinancingReceivableTroubledDebtRestructuringsTable_bacd58cd-c324-4b4d-a7b7-3b9fc48c79c7" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfFinancingReceivableTroubledDebtRestructuringsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FinancingReceivableModificationsLineItems_4bbd8dfb-cf1e-48cd-a633-5fd8b6172ed5" xlink:to="loc_us-gaap_ScheduleOfFinancingReceivableTroubledDebtRestructuringsTable_bacd58cd-c324-4b4d-a7b7-3b9fc48c79c7" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LoanRestructuringModificationAxis_90c273f1-2167-4eaa-8ce8-29517c816da1" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LoanRestructuringModificationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfFinancingReceivableTroubledDebtRestructuringsTable_bacd58cd-c324-4b4d-a7b7-3b9fc48c79c7" xlink:to="loc_us-gaap_LoanRestructuringModificationAxis_90c273f1-2167-4eaa-8ce8-29517c816da1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LoanRestructuringModificationDomain_90c273f1-2167-4eaa-8ce8-29517c816da1_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LoanRestructuringModificationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LoanRestructuringModificationAxis_90c273f1-2167-4eaa-8ce8-29517c816da1" xlink:to="loc_us-gaap_LoanRestructuringModificationDomain_90c273f1-2167-4eaa-8ce8-29517c816da1_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LoanRestructuringModificationDomain_194633b1-8a33-4257-9257-67a720d14159" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LoanRestructuringModificationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LoanRestructuringModificationAxis_90c273f1-2167-4eaa-8ce8-29517c816da1" xlink:to="loc_us-gaap_LoanRestructuringModificationDomain_194633b1-8a33-4257-9257-67a720d14159" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentDeferralMember_2dacd98a-1293-49c0-a731-1894038bc667" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PaymentDeferralMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LoanRestructuringModificationDomain_194633b1-8a33-4257-9257-67a720d14159" xlink:to="loc_us-gaap_PaymentDeferralMember_2dacd98a-1293-49c0-a731-1894038bc667" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ExtendedMaturityMember_9547e04c-9433-4d7e-98d8-367f5effd192" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ExtendedMaturityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LoanRestructuringModificationDomain_194633b1-8a33-4257-9257-67a720d14159" xlink:to="loc_us-gaap_ExtendedMaturityMember_9547e04c-9433-4d7e-98d8-367f5effd192" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractualInterestRateReductionMember_7b02ae5a-2c6f-4990-90a5-fe0146b81485" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ContractualInterestRateReductionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LoanRestructuringModificationDomain_194633b1-8a33-4257-9257-67a720d14159" xlink:to="loc_us-gaap_ContractualInterestRateReductionMember_7b02ae5a-2c6f-4990-90a5-fe0146b81485" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_fnlc_ExtendedMaturityAndPaymentDeferralMember_1569b226-c1ad-47ea-a790-6ff1c8b142c7" xlink:href="fnlc-20260331.xsd#fnlc_ExtendedMaturityAndPaymentDeferralMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LoanRestructuringModificationDomain_194633b1-8a33-4257-9257-67a720d14159" xlink:to="loc_fnlc_ExtendedMaturityAndPaymentDeferralMember_1569b226-c1ad-47ea-a790-6ff1c8b142c7" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_fnlc_ExtendedMaturityPaymentDeferralAndInterestRateReductionMember_019d756c-e2e6-75d9-8cd3-d5f5e3023c4a" xlink:href="fnlc-20260331.xsd#fnlc_ExtendedMaturityPaymentDeferralAndInterestRateReductionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LoanRestructuringModificationDomain_194633b1-8a33-4257-9257-67a720d14159" xlink:to="loc_fnlc_ExtendedMaturityPaymentDeferralAndInterestRateReductionMember_019d756c-e2e6-75d9-8cd3-d5f5e3023c4a" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis_2594465e-effe-47c7-8990-b49dde71c420" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfFinancingReceivableTroubledDebtRestructuringsTable_bacd58cd-c324-4b4d-a7b7-3b9fc48c79c7" xlink:to="loc_us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis_2594465e-effe-47c7-8990-b49dde71c420" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_2594465e-effe-47c7-8990-b49dde71c420_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis_2594465e-effe-47c7-8990-b49dde71c420" xlink:to="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_2594465e-effe-47c7-8990-b49dde71c420_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_2d8f6ea0-9ca9-45f1-b4c5-7f98f40d72b2" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis_2594465e-effe-47c7-8990-b49dde71c420" xlink:to="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_2d8f6ea0-9ca9-45f1-b4c5-7f98f40d72b2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_fnlc_RealEstateLoanOwnerOccupiedMember_aebd11e4-de1b-44d4-b411-a69b910428af" xlink:href="fnlc-20260331.xsd#fnlc_RealEstateLoanOwnerOccupiedMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_2d8f6ea0-9ca9-45f1-b4c5-7f98f40d72b2" xlink:to="loc_fnlc_RealEstateLoanOwnerOccupiedMember_aebd11e4-de1b-44d4-b411-a69b910428af" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_fnlc_RealEstateLoanNonOwnerOccupiedMember_daa3fa90-9912-419c-b532-a03f7ed38f54" xlink:href="fnlc-20260331.xsd#fnlc_RealEstateLoanNonOwnerOccupiedMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_2d8f6ea0-9ca9-45f1-b4c5-7f98f40d72b2" xlink:to="loc_fnlc_RealEstateLoanNonOwnerOccupiedMember_daa3fa90-9912-419c-b532-a03f7ed38f54" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConstructionLoansMember_21331d6b-4ea0-459b-841d-5c8a37199480" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ConstructionLoansMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_2d8f6ea0-9ca9-45f1-b4c5-7f98f40d72b2" xlink:to="loc_us-gaap_ConstructionLoansMember_21331d6b-4ea0-459b-841d-5c8a37199480" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_fnlc_CommercialAndIndustrialLoansMember_1698c749-d3b7-40a4-8c3f-3e927075f8c7" xlink:href="fnlc-20260331.xsd#fnlc_CommercialAndIndustrialLoansMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_2d8f6ea0-9ca9-45f1-b4c5-7f98f40d72b2" xlink:to="loc_fnlc_CommercialAndIndustrialLoansMember_1698c749-d3b7-40a4-8c3f-3e927075f8c7" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MultifamilyMember_2b88ac61-bdcf-46ee-8ce0-eb7062f1dc10" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_MultifamilyMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_2d8f6ea0-9ca9-45f1-b4c5-7f98f40d72b2" xlink:to="loc_srt_MultifamilyMember_2b88ac61-bdcf-46ee-8ce0-eb7062f1dc10" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_fnlc_AgricultureLoanMember_a67525ed-1813-40a1-9e6f-2072352dbcc2" xlink:href="fnlc-20260331.xsd#fnlc_AgricultureLoanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_2d8f6ea0-9ca9-45f1-b4c5-7f98f40d72b2" xlink:to="loc_fnlc_AgricultureLoanMember_a67525ed-1813-40a1-9e6f-2072352dbcc2" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_fnlc_TermLoanMember_9cde6f16-5393-493c-b913-4e99bd092ae9" xlink:href="fnlc-20260331.xsd#fnlc_TermLoanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_2d8f6ea0-9ca9-45f1-b4c5-7f98f40d72b2" xlink:to="loc_fnlc_TermLoanMember_9cde6f16-5393-493c-b913-4e99bd092ae9" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConsumerPortfolioSegmentMember_83076298-ddca-48fa-ada2-948e86bf3e8c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ConsumerPortfolioSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_2d8f6ea0-9ca9-45f1-b4c5-7f98f40d72b2" xlink:to="loc_us-gaap_ConsumerPortfolioSegmentMember_83076298-ddca-48fa-ada2-948e86bf3e8c" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivablePortfolioSegmentAxis_90337bfc-be9c-4960-98fb-dacd4ab75f9a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FinancingReceivablePortfolioSegmentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfFinancingReceivableTroubledDebtRestructuringsTable_bacd58cd-c324-4b4d-a7b7-3b9fc48c79c7" xlink:to="loc_us-gaap_FinancingReceivablePortfolioSegmentAxis_90337bfc-be9c-4960-98fb-dacd4ab75f9a" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_90337bfc-be9c-4960-98fb-dacd4ab75f9a_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FinancingReceivablePortfolioSegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FinancingReceivablePortfolioSegmentAxis_90337bfc-be9c-4960-98fb-dacd4ab75f9a" xlink:to="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_90337bfc-be9c-4960-98fb-dacd4ab75f9a_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_92541b68-61d5-4394-b8dd-7e765c82c071" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FinancingReceivablePortfolioSegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FinancingReceivablePortfolioSegmentAxis_90337bfc-be9c-4960-98fb-dacd4ab75f9a" xlink:to="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_92541b68-61d5-4394-b8dd-7e765c82c071" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommercialPortfolioSegmentMember_17bd6ecb-1cfc-4787-82bc-698558a03250" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CommercialPortfolioSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_92541b68-61d5-4394-b8dd-7e765c82c071" xlink:to="loc_us-gaap_CommercialPortfolioSegmentMember_17bd6ecb-1cfc-4787-82bc-698558a03250" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_fnlc_MunicipalPortfolioSegmentMember_f3e6e97d-cedc-4b22-aaa0-ce2971587e17" xlink:href="fnlc-20260331.xsd#fnlc_MunicipalPortfolioSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_92541b68-61d5-4394-b8dd-7e765c82c071" xlink:to="loc_fnlc_MunicipalPortfolioSegmentMember_f3e6e97d-cedc-4b22-aaa0-ce2971587e17" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ResidentialPortfolioSegmentMember_a9a7c0b5-bdc3-43ef-8153-cf1bc5b22e4a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ResidentialPortfolioSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_92541b68-61d5-4394-b8dd-7e765c82c071" xlink:to="loc_us-gaap_ResidentialPortfolioSegmentMember_a9a7c0b5-bdc3-43ef-8153-cf1bc5b22e4a" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_fnlc_HomeEquityLineOfCreditPortfolioMember_cdc32cff-34f4-45fc-8884-75c7afa273e3" xlink:href="fnlc-20260331.xsd#fnlc_HomeEquityLineOfCreditPortfolioMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_92541b68-61d5-4394-b8dd-7e765c82c071" xlink:to="loc_fnlc_HomeEquityLineOfCreditPortfolioMember_cdc32cff-34f4-45fc-8884-75c7afa273e3" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConsumerPortfolioSegmentMember_adbe52c4-5c68-4a1f-8fd4-20d9d1bf8e95" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ConsumerPortfolioSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_92541b68-61d5-4394-b8dd-7e765c82c071" xlink:to="loc_us-gaap_ConsumerPortfolioSegmentMember_adbe52c4-5c68-4a1f-8fd4-20d9d1bf8e95" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivablesPeriodPastDueAxis_e54e4b4a-4e17-44db-bfd6-4b9a0540d7e4" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FinancingReceivablesPeriodPastDueAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfFinancingReceivableTroubledDebtRestructuringsTable_bacd58cd-c324-4b4d-a7b7-3b9fc48c79c7" xlink:to="loc_us-gaap_FinancingReceivablesPeriodPastDueAxis_e54e4b4a-4e17-44db-bfd6-4b9a0540d7e4" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivablesPeriodPastDueDomain_e54e4b4a-4e17-44db-bfd6-4b9a0540d7e4_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FinancingReceivablesPeriodPastDueDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FinancingReceivablesPeriodPastDueAxis_e54e4b4a-4e17-44db-bfd6-4b9a0540d7e4" xlink:to="loc_us-gaap_FinancingReceivablesPeriodPastDueDomain_e54e4b4a-4e17-44db-bfd6-4b9a0540d7e4_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivablesPeriodPastDueDomain_399c4e5e-139a-48a0-a681-5b247e5dd984" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FinancingReceivablesPeriodPastDueDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FinancingReceivablesPeriodPastDueAxis_e54e4b4a-4e17-44db-bfd6-4b9a0540d7e4" xlink:to="loc_us-gaap_FinancingReceivablesPeriodPastDueDomain_399c4e5e-139a-48a0-a681-5b247e5dd984" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancialAssetNotPastDueMember_3baa906c-57b5-444a-899b-d215a69a7e76" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FinancialAssetNotPastDueMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivablesPeriodPastDueDomain_399c4e5e-139a-48a0-a681-5b247e5dd984" xlink:to="loc_us-gaap_FinancialAssetNotPastDueMember_3baa906c-57b5-444a-899b-d215a69a7e76" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivables30To59DaysPastDueMember_288d561b-aa66-414a-858f-31432acd7e29" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FinancingReceivables30To59DaysPastDueMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivablesPeriodPastDueDomain_399c4e5e-139a-48a0-a681-5b247e5dd984" xlink:to="loc_us-gaap_FinancingReceivables30To59DaysPastDueMember_288d561b-aa66-414a-858f-31432acd7e29" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivables60To89DaysPastDueMember_8c4df9c7-5345-4b84-bdc3-074f21c0ea62" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FinancingReceivables60To89DaysPastDueMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivablesPeriodPastDueDomain_399c4e5e-139a-48a0-a681-5b247e5dd984" xlink:to="loc_us-gaap_FinancingReceivables60To89DaysPastDueMember_8c4df9c7-5345-4b84-bdc3-074f21c0ea62" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_fnlc_ExtendedMaturityAndPaymentDeferralMember_019d2915-c573-7b97-a1a2-5eb212be7f97" xlink:href="fnlc-20260331.xsd#fnlc_ExtendedMaturityAndPaymentDeferralMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivablesPeriodPastDueDomain_399c4e5e-139a-48a0-a681-5b247e5dd984" xlink:to="loc_fnlc_ExtendedMaturityAndPaymentDeferralMember_019d2915-c573-7b97-a1a2-5eb212be7f97" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivablesEqualToGreaterThan90DaysPastDueMember_e7b03b68-244a-4e51-a417-0f18368dfce7" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FinancingReceivablesEqualToGreaterThan90DaysPastDueMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivablesPeriodPastDueDomain_399c4e5e-139a-48a0-a681-5b247e5dd984" xlink:to="loc_us-gaap_FinancingReceivablesEqualToGreaterThan90DaysPastDueMember_e7b03b68-244a-4e51-a417-0f18368dfce7" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableExcludingAccruedInterestModifiedPeriod_964702b5-acce-45db-83a4-3ed24680ad7f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FinancingReceivableExcludingAccruedInterestModifiedPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableModificationsLineItems_4bbd8dfb-cf1e-48cd-a633-5fd8b6172ed5" xlink:to="loc_us-gaap_FinancingReceivableExcludingAccruedInterestModifiedPeriod_964702b5-acce-45db-83a4-3ed24680ad7f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableModificationToTotalFinancingReceivablesExcludingAccruedInterestPercent_d9bec723-0301-4e0c-b470-62eb9b1d8aa2" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FinancingReceivableModificationToTotalFinancingReceivablesExcludingAccruedInterestPercent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableModificationsLineItems_4bbd8dfb-cf1e-48cd-a633-5fd8b6172ed5" xlink:to="loc_us-gaap_FinancingReceivableModificationToTotalFinancingReceivablesExcludingAccruedInterestPercent_d9bec723-0301-4e0c-b470-62eb9b1d8aa2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableModifiedWeightedAverageTermIncreaseFromModification_3fcc6782-2f39-4abf-9dd5-b4fdfb552270" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FinancingReceivableModifiedWeightedAverageTermIncreaseFromModification"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableModificationsLineItems_4bbd8dfb-cf1e-48cd-a633-5fd8b6172ed5" xlink:to="loc_us-gaap_FinancingReceivableModifiedWeightedAverageTermIncreaseFromModification_3fcc6782-2f39-4abf-9dd5-b4fdfb552270" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableExcludingAccruedInterestModifiedSubsequentDefault_333e8a5f-4852-497e-a51f-dcd2994297e1" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FinancingReceivableExcludingAccruedInterestModifiedSubsequentDefault"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableModificationsLineItems_4bbd8dfb-cf1e-48cd-a633-5fd8b6172ed5" xlink:to="loc_us-gaap_FinancingReceivableExcludingAccruedInterestModifiedSubsequentDefault_333e8a5f-4852-497e-a51f-dcd2994297e1" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.thefirst.com/role/AllowanceforCreditLossesNarrativeDetails" xlink:type="simple" xlink:href="fnlc-20260331.xsd#AllowanceforCreditLossesNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.thefirst.com/role/AllowanceforCreditLossesNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccountsNotesAndLoansReceivableLineItems_5686c4e9-7d16-40d2-b88f-1d8f8f392e74" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AccountsNotesAndLoansReceivableLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfAccountsNotesLoansAndFinancingReceivableTable_8c310597-9d51-42d8-9006-d595bc54a5f6" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfAccountsNotesLoansAndFinancingReceivableTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_AccountsNotesAndLoansReceivableLineItems_5686c4e9-7d16-40d2-b88f-1d8f8f392e74" xlink:to="loc_us-gaap_ScheduleOfAccountsNotesLoansAndFinancingReceivableTable_8c310597-9d51-42d8-9006-d595bc54a5f6" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivablePortfolioSegmentAxis_019d2979-d06c-7212-bf0c-5713ae6ec656" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FinancingReceivablePortfolioSegmentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfAccountsNotesLoansAndFinancingReceivableTable_8c310597-9d51-42d8-9006-d595bc54a5f6" xlink:to="loc_us-gaap_FinancingReceivablePortfolioSegmentAxis_019d2979-d06c-7212-bf0c-5713ae6ec656" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_019d2979-d06c-7212-bf0c-5713ae6ec656_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FinancingReceivablePortfolioSegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FinancingReceivablePortfolioSegmentAxis_019d2979-d06c-7212-bf0c-5713ae6ec656" xlink:to="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_019d2979-d06c-7212-bf0c-5713ae6ec656_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_019d2979-d06c-786b-bd91-3e3ee706ed7b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FinancingReceivablePortfolioSegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FinancingReceivablePortfolioSegmentAxis_019d2979-d06c-7212-bf0c-5713ae6ec656" xlink:to="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_019d2979-d06c-786b-bd91-3e3ee706ed7b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommercialPortfolioSegmentMember_019d2979-d06c-7f96-88b1-b125b1d4d8c8" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CommercialPortfolioSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_019d2979-d06c-786b-bd91-3e3ee706ed7b" xlink:to="loc_us-gaap_CommercialPortfolioSegmentMember_019d2979-d06c-7f96-88b1-b125b1d4d8c8" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ResidentialPortfolioSegmentMember_019d2979-f34e-7845-aede-307c54e578b4" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ResidentialPortfolioSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_019d2979-d06c-786b-bd91-3e3ee706ed7b" xlink:to="loc_us-gaap_ResidentialPortfolioSegmentMember_019d2979-f34e-7845-aede-307c54e578b4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_fnlc_HomeEquityLineOfCreditPortfolioMember_019d2979-f34e-70f4-a9bc-d60315f92159" xlink:href="fnlc-20260331.xsd#fnlc_HomeEquityLineOfCreditPortfolioMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_019d2979-d06c-786b-bd91-3e3ee706ed7b" xlink:to="loc_fnlc_HomeEquityLineOfCreditPortfolioMember_019d2979-f34e-70f4-a9bc-d60315f92159" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConsumerPortfolioSegmentMember_019d297a-76e0-7a68-84e3-4e3cf357703e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ConsumerPortfolioSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_019d2979-d06c-786b-bd91-3e3ee706ed7b" xlink:to="loc_us-gaap_ConsumerPortfolioSegmentMember_019d297a-76e0-7a68-84e3-4e3cf357703e" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis_019d2979-d06c-753a-b690-1993ba3ce909" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfAccountsNotesLoansAndFinancingReceivableTable_8c310597-9d51-42d8-9006-d595bc54a5f6" xlink:to="loc_us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis_019d2979-d06c-753a-b690-1993ba3ce909" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_019d2979-d06c-753a-b690-1993ba3ce909_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis_019d2979-d06c-753a-b690-1993ba3ce909" xlink:to="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_019d2979-d06c-753a-b690-1993ba3ce909_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_019d2979-d06c-7630-a568-2989c254fe1b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis_019d2979-d06c-753a-b690-1993ba3ce909" xlink:to="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_019d2979-d06c-7630-a568-2989c254fe1b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConstructionLoansMember_019d2979-d06c-739c-96a3-fc83b15418de" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ConstructionLoansMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_019d2979-d06c-7630-a568-2989c254fe1b" xlink:to="loc_us-gaap_ConstructionLoansMember_019d2979-d06c-739c-96a3-fc83b15418de" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MultifamilyMember_019d2979-d06c-72ed-b54e-77a8656f26d8" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_MultifamilyMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_019d2979-d06c-7630-a568-2989c254fe1b" xlink:to="loc_srt_MultifamilyMember_019d2979-d06c-72ed-b54e-77a8656f26d8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_fnlc_FinancingReceivablesNumberOfLoanClasses_019d2979-d06c-7291-a701-71e8b4e79e64" xlink:href="fnlc-20260331.xsd#fnlc_FinancingReceivablesNumberOfLoanClasses"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AccountsNotesAndLoansReceivableLineItems_5686c4e9-7d16-40d2-b88f-1d8f8f392e74" xlink:to="loc_fnlc_FinancingReceivablesNumberOfLoanClasses_019d2979-d06c-7291-a701-71e8b4e79e64" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_fnlc_CommercialRealEstateLoansMaximumLoanToValue_019d2979-d06c-7612-b2fe-425fbc09b0db" xlink:href="fnlc-20260331.xsd#fnlc_CommercialRealEstateLoansMaximumLoanToValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AccountsNotesAndLoansReceivableLineItems_5686c4e9-7d16-40d2-b88f-1d8f8f392e74" xlink:to="loc_fnlc_CommercialRealEstateLoansMaximumLoanToValue_019d2979-d06c-7612-b2fe-425fbc09b0db" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_fnlc_FinancingReceivableTerm_019d2979-d06c-7c04-b98b-24fa52229cd2" xlink:href="fnlc-20260331.xsd#fnlc_FinancingReceivableTerm"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AccountsNotesAndLoansReceivableLineItems_5686c4e9-7d16-40d2-b88f-1d8f8f392e74" xlink:to="loc_fnlc_FinancingReceivableTerm_019d2979-d06c-7c04-b98b-24fa52229cd2" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_fnlc_NumberOfUnitsInCommercialMultifamilyProperties_019d2979-d06c-7082-be61-fa3b0387b06d" xlink:href="fnlc-20260331.xsd#fnlc_NumberOfUnitsInCommercialMultifamilyProperties"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AccountsNotesAndLoansReceivableLineItems_5686c4e9-7d16-40d2-b88f-1d8f8f392e74" xlink:to="loc_fnlc_NumberOfUnitsInCommercialMultifamilyProperties_019d2979-d06c-7082-be61-fa3b0387b06d" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_fnlc_FinancingReceivableLoanToValueRatio_019d2979-f34e-7ef4-81d4-707d30b0761a" xlink:href="fnlc-20260331.xsd#fnlc_FinancingReceivableLoanToValueRatio"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AccountsNotesAndLoansReceivableLineItems_5686c4e9-7d16-40d2-b88f-1d8f8f392e74" xlink:to="loc_fnlc_FinancingReceivableLoanToValueRatio_019d2979-f34e-7ef4-81d4-707d30b0761a" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_fnlc_ConstructionLoansActualLoanPortfolioToCompanyCapital_019d2979-f34e-7b0a-9bf0-39d17baa6cf2" xlink:href="fnlc-20260331.xsd#fnlc_ConstructionLoansActualLoanPortfolioToCompanyCapital"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AccountsNotesAndLoansReceivableLineItems_5686c4e9-7d16-40d2-b88f-1d8f8f392e74" xlink:to="loc_fnlc_ConstructionLoansActualLoanPortfolioToCompanyCapital_019d2979-f34e-7b0a-9bf0-39d17baa6cf2" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_fnlc_ConstructionLoanPortfolioMaximumToCompanyCapital_019d2979-f34e-7a39-a451-56fa3d17804f" xlink:href="fnlc-20260331.xsd#fnlc_ConstructionLoanPortfolioMaximumToCompanyCapital"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AccountsNotesAndLoansReceivableLineItems_5686c4e9-7d16-40d2-b88f-1d8f8f392e74" xlink:to="loc_fnlc_ConstructionLoanPortfolioMaximumToCompanyCapital_019d2979-f34e-7a39-a451-56fa3d17804f" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_fnlc_ConstructionAndNonOwnerOccupiedCommercialRealEstateLoansPortfolioToCompanyCapital_019d2979-f34e-7492-bf9e-d274edd8e73f" xlink:href="fnlc-20260331.xsd#fnlc_ConstructionAndNonOwnerOccupiedCommercialRealEstateLoansPortfolioToCompanyCapital"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AccountsNotesAndLoansReceivableLineItems_5686c4e9-7d16-40d2-b88f-1d8f8f392e74" xlink:to="loc_fnlc_ConstructionAndNonOwnerOccupiedCommercialRealEstateLoansPortfolioToCompanyCapital_019d2979-f34e-7492-bf9e-d274edd8e73f" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_fnlc_ConstructionAndNonOwnerOccupiedCommercialRealEstateLoansMaximumLoanPortfolioToCompanyCapital_019d2979-f34e-7e5b-a287-c4a586cb9be7" xlink:href="fnlc-20260331.xsd#fnlc_ConstructionAndNonOwnerOccupiedCommercialRealEstateLoansMaximumLoanPortfolioToCompanyCapital"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AccountsNotesAndLoansReceivableLineItems_5686c4e9-7d16-40d2-b88f-1d8f8f392e74" xlink:to="loc_fnlc_ConstructionAndNonOwnerOccupiedCommercialRealEstateLoansMaximumLoanPortfolioToCompanyCapital_019d2979-f34e-7e5b-a287-c4a586cb9be7" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_fnlc_AllowanceforLoanLossesofTotalLoansPercentage_019d297a-1919-718c-b7ad-f7d5dbf54798" xlink:href="fnlc-20260331.xsd#fnlc_AllowanceforLoanLossesofTotalLoansPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AccountsNotesAndLoansReceivableLineItems_5686c4e9-7d16-40d2-b88f-1d8f8f392e74" xlink:to="loc_fnlc_AllowanceforLoanLossesofTotalLoansPercentage_019d297a-1919-718c-b7ad-f7d5dbf54798" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_fnlc_FinancingReceivableOutstandingLoansAndCommitmentsSubjectByIndependentConsultingFirm_019d297a-3a24-75dd-b68c-d11f5ab31d5d" xlink:href="fnlc-20260331.xsd#fnlc_FinancingReceivableOutstandingLoansAndCommitmentsSubjectByIndependentConsultingFirm"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AccountsNotesAndLoansReceivableLineItems_5686c4e9-7d16-40d2-b88f-1d8f8f392e74" xlink:to="loc_fnlc_FinancingReceivableOutstandingLoansAndCommitmentsSubjectByIndependentConsultingFirm_019d297a-3a24-75dd-b68c-d11f5ab31d5d" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_fnlc_FinancingReceivablesSubjectToAnnualInternalCreditReview_019d297a-3a24-7004-8a03-a5b734fb7802" xlink:href="fnlc-20260331.xsd#fnlc_FinancingReceivablesSubjectToAnnualInternalCreditReview"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AccountsNotesAndLoansReceivableLineItems_5686c4e9-7d16-40d2-b88f-1d8f8f392e74" xlink:to="loc_fnlc_FinancingReceivablesSubjectToAnnualInternalCreditReview_019d297a-3a24-7004-8a03-a5b734fb7802" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_fnlc_DelinquentPeriodBeforeConsumerLoansChargedOff_019d297a-76e0-7306-be50-4cd57d863967" xlink:href="fnlc-20260331.xsd#fnlc_DelinquentPeriodBeforeConsumerLoansChargedOff"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AccountsNotesAndLoansReceivableLineItems_5686c4e9-7d16-40d2-b88f-1d8f8f392e74" xlink:to="loc_fnlc_DelinquentPeriodBeforeConsumerLoansChargedOff_019d297a-76e0-7306-be50-4cd57d863967" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_fnlc_DelinquentPeriodBeforeResidentialLoansPlacedOnNonAccrualStatus_019d297a-76e0-7b3a-a95f-f9c4652c9d52" xlink:href="fnlc-20260331.xsd#fnlc_DelinquentPeriodBeforeResidentialLoansPlacedOnNonAccrualStatus"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AccountsNotesAndLoansReceivableLineItems_5686c4e9-7d16-40d2-b88f-1d8f8f392e74" xlink:to="loc_fnlc_DelinquentPeriodBeforeResidentialLoansPlacedOnNonAccrualStatus_019d297a-76e0-7b3a-a95f-f9c4652c9d52" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_fnlc_DelinquentPeriodforLoansChargedOff_019d297a-76e0-7536-b1c5-2068c73296bc" xlink:href="fnlc-20260331.xsd#fnlc_DelinquentPeriodforLoansChargedOff"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AccountsNotesAndLoansReceivableLineItems_5686c4e9-7d16-40d2-b88f-1d8f8f392e74" xlink:to="loc_fnlc_DelinquentPeriodforLoansChargedOff_019d297a-76e0-7536-b1c5-2068c73296bc" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_fnlc_DelinquentPeriodforLoansChargedOffPeriodAfterReceiptofNotificationfromBankruptcyCourt_019d297a-76e0-7c37-a929-4947f10e0046" xlink:href="fnlc-20260331.xsd#fnlc_DelinquentPeriodforLoansChargedOffPeriodAfterReceiptofNotificationfromBankruptcyCourt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AccountsNotesAndLoansReceivableLineItems_5686c4e9-7d16-40d2-b88f-1d8f8f392e74" xlink:to="loc_fnlc_DelinquentPeriodforLoansChargedOffPeriodAfterReceiptofNotificationfromBankruptcyCourt_019d297a-76e0-7c37-a929-4947f10e0046" xlink:type="arc" order="15"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.thefirst.com/role/AllowanceforCreditLossesFinancingReceivableandAllowanceElementbyClassDetails" xlink:type="simple" xlink:href="fnlc-20260331.xsd#AllowanceforCreditLossesFinancingReceivableandAllowanceElementbyClassDetails"/>
  <link:definitionLink xlink:role="http://www.thefirst.com/role/AllowanceforCreditLossesFinancingReceivableandAllowanceElementbyClassDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccountsNotesAndLoansReceivableLineItems_0f562636-99bf-45a9-b342-1f5b3093dfec" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AccountsNotesAndLoansReceivableLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfAccountsNotesLoansAndFinancingReceivableTable_fd25aae4-b8c7-4c19-8fd8-86427689b6e3" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfAccountsNotesLoansAndFinancingReceivableTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_AccountsNotesAndLoansReceivableLineItems_0f562636-99bf-45a9-b342-1f5b3093dfec" xlink:to="loc_us-gaap_ScheduleOfAccountsNotesLoansAndFinancingReceivableTable_fd25aae4-b8c7-4c19-8fd8-86427689b6e3" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivablePortfolioSegmentAxis_03f9c6ee-99eb-4683-9eff-46b54f2775ee" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FinancingReceivablePortfolioSegmentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfAccountsNotesLoansAndFinancingReceivableTable_fd25aae4-b8c7-4c19-8fd8-86427689b6e3" xlink:to="loc_us-gaap_FinancingReceivablePortfolioSegmentAxis_03f9c6ee-99eb-4683-9eff-46b54f2775ee" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_03f9c6ee-99eb-4683-9eff-46b54f2775ee_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FinancingReceivablePortfolioSegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FinancingReceivablePortfolioSegmentAxis_03f9c6ee-99eb-4683-9eff-46b54f2775ee" xlink:to="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_03f9c6ee-99eb-4683-9eff-46b54f2775ee_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_09c7933f-8346-43d3-95fa-0fb673946465" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FinancingReceivablePortfolioSegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FinancingReceivablePortfolioSegmentAxis_03f9c6ee-99eb-4683-9eff-46b54f2775ee" xlink:to="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_09c7933f-8346-43d3-95fa-0fb673946465" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommercialPortfolioSegmentMember_d29b3912-5939-4576-9f37-db9b5cd40d35" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CommercialPortfolioSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_09c7933f-8346-43d3-95fa-0fb673946465" xlink:to="loc_us-gaap_CommercialPortfolioSegmentMember_d29b3912-5939-4576-9f37-db9b5cd40d35" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_fnlc_MunicipalPortfolioSegmentMember_fc566a87-a599-4937-980f-77c0cc55e873" xlink:href="fnlc-20260331.xsd#fnlc_MunicipalPortfolioSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_09c7933f-8346-43d3-95fa-0fb673946465" xlink:to="loc_fnlc_MunicipalPortfolioSegmentMember_fc566a87-a599-4937-980f-77c0cc55e873" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ResidentialPortfolioSegmentMember_1e425e7c-43c6-4532-85ab-7d48168ba98d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ResidentialPortfolioSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_09c7933f-8346-43d3-95fa-0fb673946465" xlink:to="loc_us-gaap_ResidentialPortfolioSegmentMember_1e425e7c-43c6-4532-85ab-7d48168ba98d" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_fnlc_HomeEquityLineOfCreditPortfolioMember_84542317-cf93-4bb5-bb54-4581accc3dea" xlink:href="fnlc-20260331.xsd#fnlc_HomeEquityLineOfCreditPortfolioMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_09c7933f-8346-43d3-95fa-0fb673946465" xlink:to="loc_fnlc_HomeEquityLineOfCreditPortfolioMember_84542317-cf93-4bb5-bb54-4581accc3dea" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConsumerPortfolioSegmentMember_10473d11-53e8-46f1-a0fd-99093312c0b1" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ConsumerPortfolioSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_09c7933f-8346-43d3-95fa-0fb673946465" xlink:to="loc_us-gaap_ConsumerPortfolioSegmentMember_10473d11-53e8-46f1-a0fd-99093312c0b1" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis_55db8a90-60f8-40bb-8403-d3e86c45feea" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfAccountsNotesLoansAndFinancingReceivableTable_fd25aae4-b8c7-4c19-8fd8-86427689b6e3" xlink:to="loc_us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis_55db8a90-60f8-40bb-8403-d3e86c45feea" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_55db8a90-60f8-40bb-8403-d3e86c45feea_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis_55db8a90-60f8-40bb-8403-d3e86c45feea" xlink:to="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_55db8a90-60f8-40bb-8403-d3e86c45feea_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_d9f874ff-78d3-4b74-b1f3-91343e0e562f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis_55db8a90-60f8-40bb-8403-d3e86c45feea" xlink:to="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_d9f874ff-78d3-4b74-b1f3-91343e0e562f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RealEstateLoanMember_e4b17208-44e7-42d3-994a-9fb6be560501" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RealEstateLoanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_d9f874ff-78d3-4b74-b1f3-91343e0e562f" xlink:to="loc_us-gaap_RealEstateLoanMember_e4b17208-44e7-42d3-994a-9fb6be560501" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_fnlc_RealEstateLoanOwnerOccupiedMember_528c2772-1570-4662-9157-a780e9b713ea" xlink:href="fnlc-20260331.xsd#fnlc_RealEstateLoanOwnerOccupiedMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RealEstateLoanMember_e4b17208-44e7-42d3-994a-9fb6be560501" xlink:to="loc_fnlc_RealEstateLoanOwnerOccupiedMember_528c2772-1570-4662-9157-a780e9b713ea" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_fnlc_RealEstateLoanNonOwnerOccupiedMember_1f3d6733-e4bf-4542-b85d-4964458c6036" xlink:href="fnlc-20260331.xsd#fnlc_RealEstateLoanNonOwnerOccupiedMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RealEstateLoanMember_e4b17208-44e7-42d3-994a-9fb6be560501" xlink:to="loc_fnlc_RealEstateLoanNonOwnerOccupiedMember_1f3d6733-e4bf-4542-b85d-4964458c6036" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConstructionLoansMember_3694ec13-2d0d-4715-b432-69b06f5c462f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ConstructionLoansMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_d9f874ff-78d3-4b74-b1f3-91343e0e562f" xlink:to="loc_us-gaap_ConstructionLoansMember_3694ec13-2d0d-4715-b432-69b06f5c462f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_fnlc_CommercialAndIndustrialLoansMember_35da3ca4-beb6-4d33-b720-38f7cbc14ec3" xlink:href="fnlc-20260331.xsd#fnlc_CommercialAndIndustrialLoansMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_d9f874ff-78d3-4b74-b1f3-91343e0e562f" xlink:to="loc_fnlc_CommercialAndIndustrialLoansMember_35da3ca4-beb6-4d33-b720-38f7cbc14ec3" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MultifamilyMember_49b56429-44f1-4df1-a47f-97011d25f30d" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_MultifamilyMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_d9f874ff-78d3-4b74-b1f3-91343e0e562f" xlink:to="loc_srt_MultifamilyMember_49b56429-44f1-4df1-a47f-97011d25f30d" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_fnlc_AgricultureLoanMember_b401d3f1-096e-4458-a4c7-e030103194d2" xlink:href="fnlc-20260331.xsd#fnlc_AgricultureLoanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_d9f874ff-78d3-4b74-b1f3-91343e0e562f" xlink:to="loc_fnlc_AgricultureLoanMember_b401d3f1-096e-4458-a4c7-e030103194d2" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_fnlc_TermLoanMember_f74aea51-f37b-48a2-8d4b-4409bbc8ae52" xlink:href="fnlc-20260331.xsd#fnlc_TermLoanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_d9f874ff-78d3-4b74-b1f3-91343e0e562f" xlink:to="loc_fnlc_TermLoanMember_f74aea51-f37b-48a2-8d4b-4409bbc8ae52" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_fnlc_FinancingReceivableInformationByTypeOfReserveAxis_87ad908e-3cf2-4ce4-9737-3e7d3a900e7e" xlink:href="fnlc-20260331.xsd#fnlc_FinancingReceivableInformationByTypeOfReserveAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfAccountsNotesLoansAndFinancingReceivableTable_fd25aae4-b8c7-4c19-8fd8-86427689b6e3" xlink:to="loc_fnlc_FinancingReceivableInformationByTypeOfReserveAxis_87ad908e-3cf2-4ce4-9737-3e7d3a900e7e" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_fnlc_FinancingReceivableInformationByTypeOfReserveDomain_87ad908e-3cf2-4ce4-9737-3e7d3a900e7e_default" xlink:href="fnlc-20260331.xsd#fnlc_FinancingReceivableInformationByTypeOfReserveDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_fnlc_FinancingReceivableInformationByTypeOfReserveAxis_87ad908e-3cf2-4ce4-9737-3e7d3a900e7e" xlink:to="loc_fnlc_FinancingReceivableInformationByTypeOfReserveDomain_87ad908e-3cf2-4ce4-9737-3e7d3a900e7e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_fnlc_FinancingReceivableInformationByTypeOfReserveDomain_b277ca48-6f68-4610-8f6f-c73cca24f705" xlink:href="fnlc-20260331.xsd#fnlc_FinancingReceivableInformationByTypeOfReserveDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_fnlc_FinancingReceivableInformationByTypeOfReserveAxis_87ad908e-3cf2-4ce4-9737-3e7d3a900e7e" xlink:to="loc_fnlc_FinancingReceivableInformationByTypeOfReserveDomain_b277ca48-6f68-4610-8f6f-c73cca24f705" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_fnlc_SpecificReservesOnLoansEvaluatedIndividuallyForImpairmentMember_976337a3-a50b-4a67-b4f7-5cf951c75d4b" xlink:href="fnlc-20260331.xsd#fnlc_SpecificReservesOnLoansEvaluatedIndividuallyForImpairmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_fnlc_FinancingReceivableInformationByTypeOfReserveDomain_b277ca48-6f68-4610-8f6f-c73cca24f705" xlink:to="loc_fnlc_SpecificReservesOnLoansEvaluatedIndividuallyForImpairmentMember_976337a3-a50b-4a67-b4f7-5cf951c75d4b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_fnlc_GeneralReservesBasedOnHistoricalLossExperienceMember_3434d9fe-1687-4d2a-899f-2ce7b773ecd0" xlink:href="fnlc-20260331.xsd#fnlc_GeneralReservesBasedOnHistoricalLossExperienceMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_fnlc_FinancingReceivableInformationByTypeOfReserveDomain_b277ca48-6f68-4610-8f6f-c73cca24f705" xlink:to="loc_fnlc_GeneralReservesBasedOnHistoricalLossExperienceMember_3434d9fe-1687-4d2a-899f-2ce7b773ecd0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_fnlc_ReserveForQualitativeFactorsNettingMember_d811e2eb-248b-4735-8a40-bdaf0d3dd377" xlink:href="fnlc-20260331.xsd#fnlc_ReserveForQualitativeFactorsNettingMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_fnlc_FinancingReceivableInformationByTypeOfReserveDomain_b277ca48-6f68-4610-8f6f-c73cca24f705" xlink:to="loc_fnlc_ReserveForQualitativeFactorsNettingMember_d811e2eb-248b-4735-8a40-bdaf0d3dd377" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableAllowanceForCreditLossExcludingAccruedInterest_1d90e1d0-bd25-408f-a1be-4695f6420e19" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FinancingReceivableAllowanceForCreditLossExcludingAccruedInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AccountsNotesAndLoansReceivableLineItems_0f562636-99bf-45a9-b342-1f5b3093dfec" xlink:to="loc_us-gaap_FinancingReceivableAllowanceForCreditLossExcludingAccruedInterest_1d90e1d0-bd25-408f-a1be-4695f6420e19" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.thefirst.com/role/AllowanceforCreditLossesCreditQualityRiskRatingsbySegmentDetails" xlink:type="simple" xlink:href="fnlc-20260331.xsd#AllowanceforCreditLossesCreditQualityRiskRatingsbySegmentDetails"/>
  <link:definitionLink xlink:role="http://www.thefirst.com/role/AllowanceforCreditLossesCreditQualityRiskRatingsbySegmentDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableRecordedInvestmentLineItems_1b717de3-a2a0-405b-ae8a-5dd647ec0a75" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FinancingReceivableRecordedInvestmentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfFinancingReceivableRecordedInvestmentCreditQualityIndicatorTable_7db98ab5-86d8-44ce-93ff-cdc5eab5e183" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfFinancingReceivableRecordedInvestmentCreditQualityIndicatorTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentLineItems_1b717de3-a2a0-405b-ae8a-5dd647ec0a75" xlink:to="loc_us-gaap_ScheduleOfFinancingReceivableRecordedInvestmentCreditQualityIndicatorTable_7db98ab5-86d8-44ce-93ff-cdc5eab5e183" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivablePortfolioSegmentAxis_53585cf2-5a65-4930-8b6d-7d586066eb33" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FinancingReceivablePortfolioSegmentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfFinancingReceivableRecordedInvestmentCreditQualityIndicatorTable_7db98ab5-86d8-44ce-93ff-cdc5eab5e183" xlink:to="loc_us-gaap_FinancingReceivablePortfolioSegmentAxis_53585cf2-5a65-4930-8b6d-7d586066eb33" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_53585cf2-5a65-4930-8b6d-7d586066eb33_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FinancingReceivablePortfolioSegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FinancingReceivablePortfolioSegmentAxis_53585cf2-5a65-4930-8b6d-7d586066eb33" xlink:to="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_53585cf2-5a65-4930-8b6d-7d586066eb33_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_a4d82590-5a39-486b-bf09-cd0a6d01319f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FinancingReceivablePortfolioSegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FinancingReceivablePortfolioSegmentAxis_53585cf2-5a65-4930-8b6d-7d586066eb33" xlink:to="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_a4d82590-5a39-486b-bf09-cd0a6d01319f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommercialPortfolioSegmentMember_827d372c-b607-4ef6-9aa2-418fe0ab4bee" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CommercialPortfolioSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_a4d82590-5a39-486b-bf09-cd0a6d01319f" xlink:to="loc_us-gaap_CommercialPortfolioSegmentMember_827d372c-b607-4ef6-9aa2-418fe0ab4bee" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_fnlc_MunicipalPortfolioSegmentMember_cc82d731-21cc-4fb8-8d60-dfbf85d1894d" xlink:href="fnlc-20260331.xsd#fnlc_MunicipalPortfolioSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_a4d82590-5a39-486b-bf09-cd0a6d01319f" xlink:to="loc_fnlc_MunicipalPortfolioSegmentMember_cc82d731-21cc-4fb8-8d60-dfbf85d1894d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ResidentialPortfolioSegmentMember_573b8113-dd7a-45f2-a1b0-0e71bb22bfcc" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ResidentialPortfolioSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_a4d82590-5a39-486b-bf09-cd0a6d01319f" xlink:to="loc_us-gaap_ResidentialPortfolioSegmentMember_573b8113-dd7a-45f2-a1b0-0e71bb22bfcc" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_fnlc_HomeEquityLineOfCreditPortfolioMember_35419a31-69cd-42d1-b617-902c99881445" xlink:href="fnlc-20260331.xsd#fnlc_HomeEquityLineOfCreditPortfolioMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_a4d82590-5a39-486b-bf09-cd0a6d01319f" xlink:to="loc_fnlc_HomeEquityLineOfCreditPortfolioMember_35419a31-69cd-42d1-b617-902c99881445" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConsumerPortfolioSegmentMember_dc71ed40-4f3e-4195-8dd4-2de641c6d317" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ConsumerPortfolioSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_a4d82590-5a39-486b-bf09-cd0a6d01319f" xlink:to="loc_us-gaap_ConsumerPortfolioSegmentMember_dc71ed40-4f3e-4195-8dd4-2de641c6d317" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis_42c4a9d9-bdc3-42c3-aa49-0e01729a100c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfFinancingReceivableRecordedInvestmentCreditQualityIndicatorTable_7db98ab5-86d8-44ce-93ff-cdc5eab5e183" xlink:to="loc_us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis_42c4a9d9-bdc3-42c3-aa49-0e01729a100c" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_42c4a9d9-bdc3-42c3-aa49-0e01729a100c_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis_42c4a9d9-bdc3-42c3-aa49-0e01729a100c" xlink:to="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_42c4a9d9-bdc3-42c3-aa49-0e01729a100c_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_4706627a-4d8d-41a3-98ad-6691040257aa" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis_42c4a9d9-bdc3-42c3-aa49-0e01729a100c" xlink:to="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_4706627a-4d8d-41a3-98ad-6691040257aa" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_fnlc_RealEstateLoanOwnerOccupiedMember_1b55a5fb-d364-48d3-b313-8119acb0f53d" xlink:href="fnlc-20260331.xsd#fnlc_RealEstateLoanOwnerOccupiedMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_4706627a-4d8d-41a3-98ad-6691040257aa" xlink:to="loc_fnlc_RealEstateLoanOwnerOccupiedMember_1b55a5fb-d364-48d3-b313-8119acb0f53d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_fnlc_RealEstateLoanNonOwnerOccupiedMember_263d707d-037e-4d7f-9244-55e1dc4eb889" xlink:href="fnlc-20260331.xsd#fnlc_RealEstateLoanNonOwnerOccupiedMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_4706627a-4d8d-41a3-98ad-6691040257aa" xlink:to="loc_fnlc_RealEstateLoanNonOwnerOccupiedMember_263d707d-037e-4d7f-9244-55e1dc4eb889" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConstructionLoansMember_1f272067-d434-4b39-b943-4c071cdfabb7" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ConstructionLoansMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_4706627a-4d8d-41a3-98ad-6691040257aa" xlink:to="loc_us-gaap_ConstructionLoansMember_1f272067-d434-4b39-b943-4c071cdfabb7" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_fnlc_CommercialAndIndustrialLoansMember_4520391e-eb65-4597-bdce-fd9169135267" xlink:href="fnlc-20260331.xsd#fnlc_CommercialAndIndustrialLoansMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_4706627a-4d8d-41a3-98ad-6691040257aa" xlink:to="loc_fnlc_CommercialAndIndustrialLoansMember_4520391e-eb65-4597-bdce-fd9169135267" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MultifamilyMember_a9dc409e-86f6-4396-8bde-73cd6b91166b" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_MultifamilyMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_4706627a-4d8d-41a3-98ad-6691040257aa" xlink:to="loc_srt_MultifamilyMember_a9dc409e-86f6-4396-8bde-73cd6b91166b" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_fnlc_AgricultureLoanMember_204dc7bd-8cb8-4ece-a2d5-d5a471ad7e63" xlink:href="fnlc-20260331.xsd#fnlc_AgricultureLoanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_4706627a-4d8d-41a3-98ad-6691040257aa" xlink:to="loc_fnlc_AgricultureLoanMember_204dc7bd-8cb8-4ece-a2d5-d5a471ad7e63" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_fnlc_TermLoanMember_ea02bce7-ae41-45f5-bfc3-4ddcd963146f" xlink:href="fnlc-20260331.xsd#fnlc_TermLoanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_4706627a-4d8d-41a3-98ad-6691040257aa" xlink:to="loc_fnlc_TermLoanMember_ea02bce7-ae41-45f5-bfc3-4ddcd963146f" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InternalCreditAssessmentAxis_7c7f7d12-8d59-4543-91ac-4de3dee886f8" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_InternalCreditAssessmentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfFinancingReceivableRecordedInvestmentCreditQualityIndicatorTable_7db98ab5-86d8-44ce-93ff-cdc5eab5e183" xlink:to="loc_us-gaap_InternalCreditAssessmentAxis_7c7f7d12-8d59-4543-91ac-4de3dee886f8" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InternalCreditAssessmentDomain_7c7f7d12-8d59-4543-91ac-4de3dee886f8_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_InternalCreditAssessmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_InternalCreditAssessmentAxis_7c7f7d12-8d59-4543-91ac-4de3dee886f8" xlink:to="loc_us-gaap_InternalCreditAssessmentDomain_7c7f7d12-8d59-4543-91ac-4de3dee886f8_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InternalCreditAssessmentDomain_5cbe2b59-2d33-43e8-acce-7ffd24ddae9a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_InternalCreditAssessmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_InternalCreditAssessmentAxis_7c7f7d12-8d59-4543-91ac-4de3dee886f8" xlink:to="loc_us-gaap_InternalCreditAssessmentDomain_5cbe2b59-2d33-43e8-acce-7ffd24ddae9a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_fnlc_RiskRatedMember_5056faae-a2e1-4c3a-addf-0cdea0bae629" xlink:href="fnlc-20260331.xsd#fnlc_RiskRatedMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InternalCreditAssessmentDomain_5cbe2b59-2d33-43e8-acce-7ffd24ddae9a" xlink:to="loc_fnlc_RiskRatedMember_5056faae-a2e1-4c3a-addf-0cdea0bae629" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PassMember_895262bc-9358-4e26-93bd-bc377defcd7c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PassMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_fnlc_RiskRatedMember_5056faae-a2e1-4c3a-addf-0cdea0bae629" xlink:to="loc_us-gaap_PassMember_895262bc-9358-4e26-93bd-bc377defcd7c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SpecialMentionMember_86fa30ed-8a1f-45b5-9f15-c83841f6bb12" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SpecialMentionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_fnlc_RiskRatedMember_5056faae-a2e1-4c3a-addf-0cdea0bae629" xlink:to="loc_us-gaap_SpecialMentionMember_86fa30ed-8a1f-45b5-9f15-c83841f6bb12" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubstandardMember_08af70b2-0224-4d8f-bb99-74f4b95f491c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SubstandardMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_fnlc_RiskRatedMember_5056faae-a2e1-4c3a-addf-0cdea0bae629" xlink:to="loc_us-gaap_SubstandardMember_08af70b2-0224-4d8f-bb99-74f4b95f491c" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DoubtfulMember_ac68e4a3-0e12-4786-8c38-8bcfcfbcd5c2" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DoubtfulMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_fnlc_RiskRatedMember_5056faae-a2e1-4c3a-addf-0cdea0bae629" xlink:to="loc_us-gaap_DoubtfulMember_ac68e4a3-0e12-4786-8c38-8bcfcfbcd5c2" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableExcludingAccruedInterestBeforeAllowanceForCreditLossByOriginationYearAbstract_1cdd9f6d-6264-440a-8272-5fcbafe25899" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FinancingReceivableExcludingAccruedInterestBeforeAllowanceForCreditLossByOriginationYearAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentLineItems_1b717de3-a2a0-405b-ae8a-5dd647ec0a75" xlink:to="loc_us-gaap_FinancingReceivableExcludingAccruedInterestBeforeAllowanceForCreditLossByOriginationYearAbstract_1cdd9f6d-6264-440a-8272-5fcbafe25899" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableExcludingAccruedInterestYearOneOriginatedCurrentFiscalYear_967f5d0a-2619-4938-87d7-e72e6eb0a05f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FinancingReceivableExcludingAccruedInterestYearOneOriginatedCurrentFiscalYear"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableExcludingAccruedInterestBeforeAllowanceForCreditLossByOriginationYearAbstract_1cdd9f6d-6264-440a-8272-5fcbafe25899" xlink:to="loc_us-gaap_FinancingReceivableExcludingAccruedInterestYearOneOriginatedCurrentFiscalYear_967f5d0a-2619-4938-87d7-e72e6eb0a05f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableExcludingAccruedInterestYearTwoOriginatedFiscalYearBeforeCurrentFiscalYear_071da86e-c725-4b62-a794-800e4684c8af" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FinancingReceivableExcludingAccruedInterestYearTwoOriginatedFiscalYearBeforeCurrentFiscalYear"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableExcludingAccruedInterestBeforeAllowanceForCreditLossByOriginationYearAbstract_1cdd9f6d-6264-440a-8272-5fcbafe25899" xlink:to="loc_us-gaap_FinancingReceivableExcludingAccruedInterestYearTwoOriginatedFiscalYearBeforeCurrentFiscalYear_071da86e-c725-4b62-a794-800e4684c8af" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableExcludingAccruedInterestYearThreeOriginatedTwoYearsBeforeCurrentFiscalYear_c71f91a4-5278-459c-ab1b-12f382880573" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FinancingReceivableExcludingAccruedInterestYearThreeOriginatedTwoYearsBeforeCurrentFiscalYear"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableExcludingAccruedInterestBeforeAllowanceForCreditLossByOriginationYearAbstract_1cdd9f6d-6264-440a-8272-5fcbafe25899" xlink:to="loc_us-gaap_FinancingReceivableExcludingAccruedInterestYearThreeOriginatedTwoYearsBeforeCurrentFiscalYear_c71f91a4-5278-459c-ab1b-12f382880573" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableExcludingAccruedInterestYearFourOriginatedThreeYearsBeforeCurrentFiscalYear_86841cd5-f079-4f0a-b332-48f5cad4ceda" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FinancingReceivableExcludingAccruedInterestYearFourOriginatedThreeYearsBeforeCurrentFiscalYear"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableExcludingAccruedInterestBeforeAllowanceForCreditLossByOriginationYearAbstract_1cdd9f6d-6264-440a-8272-5fcbafe25899" xlink:to="loc_us-gaap_FinancingReceivableExcludingAccruedInterestYearFourOriginatedThreeYearsBeforeCurrentFiscalYear_86841cd5-f079-4f0a-b332-48f5cad4ceda" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableExcludingAccruedInterestYearFiveOriginatedFourYearsBeforeCurrentFiscalYear_b6f24635-699e-45fe-bcbb-2a5a3c81151a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FinancingReceivableExcludingAccruedInterestYearFiveOriginatedFourYearsBeforeCurrentFiscalYear"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableExcludingAccruedInterestBeforeAllowanceForCreditLossByOriginationYearAbstract_1cdd9f6d-6264-440a-8272-5fcbafe25899" xlink:to="loc_us-gaap_FinancingReceivableExcludingAccruedInterestYearFiveOriginatedFourYearsBeforeCurrentFiscalYear_b6f24635-699e-45fe-bcbb-2a5a3c81151a" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableExcludingAccruedInterestOriginatedMoreThanFiveYearsBeforeCurrentFiscalYear_d698d872-3190-4061-b3df-fd4b5e561db0" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FinancingReceivableExcludingAccruedInterestOriginatedMoreThanFiveYearsBeforeCurrentFiscalYear"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableExcludingAccruedInterestBeforeAllowanceForCreditLossByOriginationYearAbstract_1cdd9f6d-6264-440a-8272-5fcbafe25899" xlink:to="loc_us-gaap_FinancingReceivableExcludingAccruedInterestOriginatedMoreThanFiveYearsBeforeCurrentFiscalYear_d698d872-3190-4061-b3df-fd4b5e561db0" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableExcludingAccruedInterestRevolving_08b98122-b17b-4a52-ac01-4eff769fc0a3" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FinancingReceivableExcludingAccruedInterestRevolving"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableExcludingAccruedInterestBeforeAllowanceForCreditLossByOriginationYearAbstract_1cdd9f6d-6264-440a-8272-5fcbafe25899" xlink:to="loc_us-gaap_FinancingReceivableExcludingAccruedInterestRevolving_08b98122-b17b-4a52-ac01-4eff769fc0a3" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableExcludingAccruedInterestRevolvingConvertedToTermLoan_16a6e6bc-8156-4025-b564-cbf64397fbfc" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FinancingReceivableExcludingAccruedInterestRevolvingConvertedToTermLoan"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableExcludingAccruedInterestBeforeAllowanceForCreditLossByOriginationYearAbstract_1cdd9f6d-6264-440a-8272-5fcbafe25899" xlink:to="loc_us-gaap_FinancingReceivableExcludingAccruedInterestRevolvingConvertedToTermLoan_16a6e6bc-8156-4025-b564-cbf64397fbfc" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableExcludingAccruedInterestBeforeAllowanceForCreditLoss_0490647f-4d2d-4d73-9dc6-025d7b43165f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FinancingReceivableExcludingAccruedInterestBeforeAllowanceForCreditLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableExcludingAccruedInterestBeforeAllowanceForCreditLossByOriginationYearAbstract_1cdd9f6d-6264-440a-8272-5fcbafe25899" xlink:to="loc_us-gaap_FinancingReceivableExcludingAccruedInterestBeforeAllowanceForCreditLoss_0490647f-4d2d-4d73-9dc6-025d7b43165f" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableExcludingAccruedInterestAllowanceForCreditLossWriteoffAfterRecoveryAbstract_9db84445-804c-4cd4-b141-13ea82f3cfac" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FinancingReceivableExcludingAccruedInterestAllowanceForCreditLossWriteoffAfterRecoveryAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentLineItems_1b717de3-a2a0-405b-ae8a-5dd647ec0a75" xlink:to="loc_us-gaap_FinancingReceivableExcludingAccruedInterestAllowanceForCreditLossWriteoffAfterRecoveryAbstract_9db84445-804c-4cd4-b141-13ea82f3cfac" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableExcludingAccruedInterestYearOneOriginatedCurrentFiscalYearWriteoff_e5e85236-be73-490e-b1aa-dad024ba1dd8" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FinancingReceivableExcludingAccruedInterestYearOneOriginatedCurrentFiscalYearWriteoff"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableExcludingAccruedInterestAllowanceForCreditLossWriteoffAfterRecoveryAbstract_9db84445-804c-4cd4-b141-13ea82f3cfac" xlink:to="loc_us-gaap_FinancingReceivableExcludingAccruedInterestYearOneOriginatedCurrentFiscalYearWriteoff_e5e85236-be73-490e-b1aa-dad024ba1dd8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableExcludingAccruedInterestYearTwoOriginatedFiscalYearBeforeCurrentFiscalYearWriteoff_2068a7b2-b015-46db-aaf2-8e47f6ee038e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FinancingReceivableExcludingAccruedInterestYearTwoOriginatedFiscalYearBeforeCurrentFiscalYearWriteoff"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableExcludingAccruedInterestAllowanceForCreditLossWriteoffAfterRecoveryAbstract_9db84445-804c-4cd4-b141-13ea82f3cfac" xlink:to="loc_us-gaap_FinancingReceivableExcludingAccruedInterestYearTwoOriginatedFiscalYearBeforeCurrentFiscalYearWriteoff_2068a7b2-b015-46db-aaf2-8e47f6ee038e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableExcludingAccruedInterestYearThreeOriginatedTwoYearsBeforeCurrentFiscalYearWriteoff_194238a6-2c43-4887-89cf-d9b896b245f2" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FinancingReceivableExcludingAccruedInterestYearThreeOriginatedTwoYearsBeforeCurrentFiscalYearWriteoff"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableExcludingAccruedInterestAllowanceForCreditLossWriteoffAfterRecoveryAbstract_9db84445-804c-4cd4-b141-13ea82f3cfac" xlink:to="loc_us-gaap_FinancingReceivableExcludingAccruedInterestYearThreeOriginatedTwoYearsBeforeCurrentFiscalYearWriteoff_194238a6-2c43-4887-89cf-d9b896b245f2" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableExcludingAccruedInterestYearFourOriginatedThreeYearsBeforeCurrentFiscalYearWriteoff_fbda7ffe-e511-43e2-9747-4f9b1e91ab79" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FinancingReceivableExcludingAccruedInterestYearFourOriginatedThreeYearsBeforeCurrentFiscalYearWriteoff"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableExcludingAccruedInterestAllowanceForCreditLossWriteoffAfterRecoveryAbstract_9db84445-804c-4cd4-b141-13ea82f3cfac" xlink:to="loc_us-gaap_FinancingReceivableExcludingAccruedInterestYearFourOriginatedThreeYearsBeforeCurrentFiscalYearWriteoff_fbda7ffe-e511-43e2-9747-4f9b1e91ab79" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableExcludingAccruedInterestYearFiveOriginatedFourYearsBeforeCurrentFiscalYearWriteoff_f8f6adc0-9832-4750-a9b7-82dea1e05446" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FinancingReceivableExcludingAccruedInterestYearFiveOriginatedFourYearsBeforeCurrentFiscalYearWriteoff"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableExcludingAccruedInterestAllowanceForCreditLossWriteoffAfterRecoveryAbstract_9db84445-804c-4cd4-b141-13ea82f3cfac" xlink:to="loc_us-gaap_FinancingReceivableExcludingAccruedInterestYearFiveOriginatedFourYearsBeforeCurrentFiscalYearWriteoff_f8f6adc0-9832-4750-a9b7-82dea1e05446" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableExcludingAccruedInterestOriginatedMoreThanFiveYearsBeforeCurrentFiscalYearWriteoff_447e300b-b64d-4808-bd0c-99060dcc7f8c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FinancingReceivableExcludingAccruedInterestOriginatedMoreThanFiveYearsBeforeCurrentFiscalYearWriteoff"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableExcludingAccruedInterestAllowanceForCreditLossWriteoffAfterRecoveryAbstract_9db84445-804c-4cd4-b141-13ea82f3cfac" xlink:to="loc_us-gaap_FinancingReceivableExcludingAccruedInterestOriginatedMoreThanFiveYearsBeforeCurrentFiscalYearWriteoff_447e300b-b64d-4808-bd0c-99060dcc7f8c" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableExcludingAccruedInterestRevolvingWriteoff_0f0bd13e-ff1c-4ff6-942f-11e9ccedc119" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FinancingReceivableExcludingAccruedInterestRevolvingWriteoff"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableExcludingAccruedInterestAllowanceForCreditLossWriteoffAfterRecoveryAbstract_9db84445-804c-4cd4-b141-13ea82f3cfac" xlink:to="loc_us-gaap_FinancingReceivableExcludingAccruedInterestRevolvingWriteoff_0f0bd13e-ff1c-4ff6-942f-11e9ccedc119" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableExcludingAccruedInterestRevolvingConvertedToTermLoanWriteoff_76b0fcfb-2038-4e52-9e07-2ab7c9102e48" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FinancingReceivableExcludingAccruedInterestRevolvingConvertedToTermLoanWriteoff"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableExcludingAccruedInterestAllowanceForCreditLossWriteoffAfterRecoveryAbstract_9db84445-804c-4cd4-b141-13ea82f3cfac" xlink:to="loc_us-gaap_FinancingReceivableExcludingAccruedInterestRevolvingConvertedToTermLoanWriteoff_76b0fcfb-2038-4e52-9e07-2ab7c9102e48" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableExcludingAccruedInterestAllowanceForCreditLossWriteoff_810f7b6e-e8f3-46f1-80b6-71f01e3a9934" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FinancingReceivableExcludingAccruedInterestAllowanceForCreditLossWriteoff"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableExcludingAccruedInterestAllowanceForCreditLossWriteoffAfterRecoveryAbstract_9db84445-804c-4cd4-b141-13ea82f3cfac" xlink:to="loc_us-gaap_FinancingReceivableExcludingAccruedInterestAllowanceForCreditLossWriteoff_810f7b6e-e8f3-46f1-80b6-71f01e3a9934" xlink:type="arc" order="9"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.thefirst.com/role/AllowanceforCreditLossesActivitybyClassDetails" xlink:type="simple" xlink:href="fnlc-20260331.xsd#AllowanceforCreditLossesActivitybyClassDetails"/>
  <link:definitionLink xlink:role="http://www.thefirst.com/role/AllowanceforCreditLossesActivitybyClassDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccountsNotesAndLoansReceivableLineItems_f427a327-5575-4b07-81c5-976b972ebc95" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AccountsNotesAndLoansReceivableLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfAccountsNotesLoansAndFinancingReceivableTable_5d58dda3-e2d9-4eb4-8037-d3ec8b94b271" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfAccountsNotesLoansAndFinancingReceivableTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_AccountsNotesAndLoansReceivableLineItems_f427a327-5575-4b07-81c5-976b972ebc95" xlink:to="loc_us-gaap_ScheduleOfAccountsNotesLoansAndFinancingReceivableTable_5d58dda3-e2d9-4eb4-8037-d3ec8b94b271" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivablePortfolioSegmentAxis_7e350c7c-14af-496f-81a5-5e689c6452ec" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FinancingReceivablePortfolioSegmentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfAccountsNotesLoansAndFinancingReceivableTable_5d58dda3-e2d9-4eb4-8037-d3ec8b94b271" xlink:to="loc_us-gaap_FinancingReceivablePortfolioSegmentAxis_7e350c7c-14af-496f-81a5-5e689c6452ec" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_7e350c7c-14af-496f-81a5-5e689c6452ec_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FinancingReceivablePortfolioSegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FinancingReceivablePortfolioSegmentAxis_7e350c7c-14af-496f-81a5-5e689c6452ec" xlink:to="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_7e350c7c-14af-496f-81a5-5e689c6452ec_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_490b5113-f554-4fc6-bea1-c729e7e96256" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FinancingReceivablePortfolioSegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FinancingReceivablePortfolioSegmentAxis_7e350c7c-14af-496f-81a5-5e689c6452ec" xlink:to="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_490b5113-f554-4fc6-bea1-c729e7e96256" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommercialPortfolioSegmentMember_b589d394-100b-4a03-a632-ba60f08f9b73" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CommercialPortfolioSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_490b5113-f554-4fc6-bea1-c729e7e96256" xlink:to="loc_us-gaap_CommercialPortfolioSegmentMember_b589d394-100b-4a03-a632-ba60f08f9b73" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_fnlc_MunicipalPortfolioSegmentMember_c1b04ee9-003c-43f3-a466-b969f186d36b" xlink:href="fnlc-20260331.xsd#fnlc_MunicipalPortfolioSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_490b5113-f554-4fc6-bea1-c729e7e96256" xlink:to="loc_fnlc_MunicipalPortfolioSegmentMember_c1b04ee9-003c-43f3-a466-b969f186d36b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ResidentialPortfolioSegmentMember_121e8ba9-c112-4cf9-b33d-12520533b717" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ResidentialPortfolioSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_490b5113-f554-4fc6-bea1-c729e7e96256" xlink:to="loc_us-gaap_ResidentialPortfolioSegmentMember_121e8ba9-c112-4cf9-b33d-12520533b717" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_fnlc_HomeEquityLineOfCreditPortfolioMember_d61fd736-30f3-4a3e-9add-265c3ccad5f8" xlink:href="fnlc-20260331.xsd#fnlc_HomeEquityLineOfCreditPortfolioMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_490b5113-f554-4fc6-bea1-c729e7e96256" xlink:to="loc_fnlc_HomeEquityLineOfCreditPortfolioMember_d61fd736-30f3-4a3e-9add-265c3ccad5f8" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConsumerPortfolioSegmentMember_43e9161d-6a2e-49d7-a0d2-8f1ae5c2bb87" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ConsumerPortfolioSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_490b5113-f554-4fc6-bea1-c729e7e96256" xlink:to="loc_us-gaap_ConsumerPortfolioSegmentMember_43e9161d-6a2e-49d7-a0d2-8f1ae5c2bb87" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis_35f3bf59-b1bc-492a-a298-3349e752cb30" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfAccountsNotesLoansAndFinancingReceivableTable_5d58dda3-e2d9-4eb4-8037-d3ec8b94b271" xlink:to="loc_us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis_35f3bf59-b1bc-492a-a298-3349e752cb30" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_35f3bf59-b1bc-492a-a298-3349e752cb30_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis_35f3bf59-b1bc-492a-a298-3349e752cb30" xlink:to="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_35f3bf59-b1bc-492a-a298-3349e752cb30_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_45bb1e45-ee76-4956-902c-1ea0977c23ca" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis_35f3bf59-b1bc-492a-a298-3349e752cb30" xlink:to="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_45bb1e45-ee76-4956-902c-1ea0977c23ca" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RealEstateLoanMember_7696acac-4bbf-4d82-b3cf-0deec0059bb4" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RealEstateLoanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_45bb1e45-ee76-4956-902c-1ea0977c23ca" xlink:to="loc_us-gaap_RealEstateLoanMember_7696acac-4bbf-4d82-b3cf-0deec0059bb4" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_fnlc_RealEstateLoanOwnerOccupiedMember_d8437a49-d18d-42c3-a6c1-dca824149d16" xlink:href="fnlc-20260331.xsd#fnlc_RealEstateLoanOwnerOccupiedMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RealEstateLoanMember_7696acac-4bbf-4d82-b3cf-0deec0059bb4" xlink:to="loc_fnlc_RealEstateLoanOwnerOccupiedMember_d8437a49-d18d-42c3-a6c1-dca824149d16" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_fnlc_RealEstateLoanNonOwnerOccupiedMember_f54cbaa6-c5a5-4782-a38d-7a12cf3f1ab2" xlink:href="fnlc-20260331.xsd#fnlc_RealEstateLoanNonOwnerOccupiedMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RealEstateLoanMember_7696acac-4bbf-4d82-b3cf-0deec0059bb4" xlink:to="loc_fnlc_RealEstateLoanNonOwnerOccupiedMember_f54cbaa6-c5a5-4782-a38d-7a12cf3f1ab2" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConstructionLoansMember_3379a33a-6e39-43ae-b11e-50e8fc07f69c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ConstructionLoansMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_45bb1e45-ee76-4956-902c-1ea0977c23ca" xlink:to="loc_us-gaap_ConstructionLoansMember_3379a33a-6e39-43ae-b11e-50e8fc07f69c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_fnlc_CommercialAndIndustrialLoansMember_014973eb-2007-4e82-ae9c-76848ba33b88" xlink:href="fnlc-20260331.xsd#fnlc_CommercialAndIndustrialLoansMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_45bb1e45-ee76-4956-902c-1ea0977c23ca" xlink:to="loc_fnlc_CommercialAndIndustrialLoansMember_014973eb-2007-4e82-ae9c-76848ba33b88" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MultifamilyMember_bd0d2bc2-0eaf-4a7c-9a59-7a64552feb86" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_MultifamilyMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_45bb1e45-ee76-4956-902c-1ea0977c23ca" xlink:to="loc_srt_MultifamilyMember_bd0d2bc2-0eaf-4a7c-9a59-7a64552feb86" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_fnlc_AgricultureLoanMember_5b385b69-4de5-4f54-b3b0-b323f8782ede" xlink:href="fnlc-20260331.xsd#fnlc_AgricultureLoanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_45bb1e45-ee76-4956-902c-1ea0977c23ca" xlink:to="loc_fnlc_AgricultureLoanMember_5b385b69-4de5-4f54-b3b0-b323f8782ede" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_fnlc_TermLoanMember_8c92f2aa-00e1-42c6-b47c-936f4b222edd" xlink:href="fnlc-20260331.xsd#fnlc_TermLoanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_45bb1e45-ee76-4956-902c-1ea0977c23ca" xlink:to="loc_fnlc_TermLoanMember_8c92f2aa-00e1-42c6-b47c-936f4b222edd" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AllowanceForLoanAndLeaseLossesRollForward_8db8f193-5ab1-4504-aa17-4776c29090f5" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AllowanceForLoanAndLeaseLossesRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AccountsNotesAndLoansReceivableLineItems_f427a327-5575-4b07-81c5-976b972ebc95" xlink:to="loc_us-gaap_AllowanceForLoanAndLeaseLossesRollForward_8db8f193-5ab1-4504-aa17-4776c29090f5" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableAllowanceForCreditLossExcludingAccruedInterest_70ec6e6b-8e28-4655-ab98-086a5977e941" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FinancingReceivableAllowanceForCreditLossExcludingAccruedInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AllowanceForLoanAndLeaseLossesRollForward_8db8f193-5ab1-4504-aa17-4776c29090f5" xlink:to="loc_us-gaap_FinancingReceivableAllowanceForCreditLossExcludingAccruedInterest_70ec6e6b-8e28-4655-ab98-086a5977e941" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableExcludingAccruedInterestAllowanceForCreditLossWriteoff_f7a97222-6421-407d-a5d0-0851a982b4ce" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FinancingReceivableExcludingAccruedInterestAllowanceForCreditLossWriteoff"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AllowanceForLoanAndLeaseLossesRollForward_8db8f193-5ab1-4504-aa17-4776c29090f5" xlink:to="loc_us-gaap_FinancingReceivableExcludingAccruedInterestAllowanceForCreditLossWriteoff_f7a97222-6421-407d-a5d0-0851a982b4ce" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableExcludingAccruedInterestAllowanceForCreditLossRecovery_17e0127b-3c86-432e-9fc9-54e655b79fe8" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FinancingReceivableExcludingAccruedInterestAllowanceForCreditLossRecovery"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AllowanceForLoanAndLeaseLossesRollForward_8db8f193-5ab1-4504-aa17-4776c29090f5" xlink:to="loc_us-gaap_FinancingReceivableExcludingAccruedInterestAllowanceForCreditLossRecovery_17e0127b-3c86-432e-9fc9-54e655b79fe8" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableExcludingAccruedInterestCreditLossExpenseReversal_c6c7a2ab-0239-4f43-8746-1e04efc112ad" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FinancingReceivableExcludingAccruedInterestCreditLossExpenseReversal"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AllowanceForLoanAndLeaseLossesRollForward_8db8f193-5ab1-4504-aa17-4776c29090f5" xlink:to="loc_us-gaap_FinancingReceivableExcludingAccruedInterestCreditLossExpenseReversal_c6c7a2ab-0239-4f43-8746-1e04efc112ad" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableAllowanceForCreditLossExcludingAccruedInterest_3a92ba21-aa59-4e5f-8a30-6f0ede5e5fc5" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FinancingReceivableAllowanceForCreditLossExcludingAccruedInterest"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.thefirst.com/role/StockBasedCompensationNarrativeDetails" xlink:type="simple" xlink:href="fnlc-20260331.xsd#StockBasedCompensationNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.thefirst.com/role/StockBasedCompensationNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_c6c4032f-45cf-4a6c-ab6a-39b8f60f10f1" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_d238a218-e400-4da4-a8e9-fb4f663a3b17" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_c6c4032f-45cf-4a6c-ab6a-39b8f60f10f1" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_d238a218-e400-4da4-a8e9-fb4f663a3b17" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameAxis_c77a8fc8-8e82-45cd-b353-4885b6fb14ae" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PlanNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_d238a218-e400-4da4-a8e9-fb4f663a3b17" xlink:to="loc_us-gaap_PlanNameAxis_c77a8fc8-8e82-45cd-b353-4885b6fb14ae" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameDomain_c77a8fc8-8e82-45cd-b353-4885b6fb14ae_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PlanNameAxis_c77a8fc8-8e82-45cd-b353-4885b6fb14ae" xlink:to="loc_us-gaap_PlanNameDomain_c77a8fc8-8e82-45cd-b353-4885b6fb14ae_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameDomain_04382512-ffaa-4880-a588-3f0d41df7f2b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PlanNameAxis_c77a8fc8-8e82-45cd-b353-4885b6fb14ae" xlink:to="loc_us-gaap_PlanNameDomain_04382512-ffaa-4880-a588-3f0d41df7f2b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_fnlc_A2020EquityIncentivePlanMember_222ef610-1f71-4170-8c6d-207ad802dd17" xlink:href="fnlc-20260331.xsd#fnlc_A2020EquityIncentivePlanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PlanNameDomain_04382512-ffaa-4880-a588-3f0d41df7f2b" xlink:to="loc_fnlc_A2020EquityIncentivePlanMember_222ef610-1f71-4170-8c6d-207ad802dd17" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_b97e01e5-2211-4a66-bc2b-7496ba119ca4" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_d238a218-e400-4da4-a8e9-fb4f663a3b17" xlink:to="loc_us-gaap_AwardTypeAxis_b97e01e5-2211-4a66-bc2b-7496ba119ca4" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_b97e01e5-2211-4a66-bc2b-7496ba119ca4_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_b97e01e5-2211-4a66-bc2b-7496ba119ca4" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_b97e01e5-2211-4a66-bc2b-7496ba119ca4_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_7d4f8c76-02a3-4ea1-b1d3-57c2a4e8023a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_b97e01e5-2211-4a66-bc2b-7496ba119ca4" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_7d4f8c76-02a3-4ea1-b1d3-57c2a4e8023a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockMember_f36a4de9-fead-445d-bc04-8efdb53fc81f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RestrictedStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_7d4f8c76-02a3-4ea1-b1d3-57c2a4e8023a" xlink:to="loc_us-gaap_RestrictedStockMember_f36a4de9-fead-445d-bc04-8efdb53fc81f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockCapitalSharesReservedForFutureIssuance_a39b85f9-bdc9-453f-ac6c-79ea0f9d7c2b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CommonStockCapitalSharesReservedForFutureIssuance"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_c6c4032f-45cf-4a6c-ab6a-39b8f60f10f1" xlink:to="loc_us-gaap_CommonStockCapitalSharesReservedForFutureIssuance_a39b85f9-bdc9-453f-ac6c-79ea0f9d7c2b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_878affc3-674e-452a-9bb1-a796c07a9bc2" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_c6c4032f-45cf-4a6c-ab6a-39b8f60f10f1" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_878affc3-674e-452a-9bb1-a796c07a9bc2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_fnlc_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostRecognizedAndNotYetRecognized_fbb5a473-d0ab-4bae-bfee-dc34d4f855cf" xlink:href="fnlc-20260331.xsd#fnlc_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostRecognizedAndNotYetRecognized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_c6c4032f-45cf-4a6c-ab6a-39b8f60f10f1" xlink:to="loc_fnlc_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostRecognizedAndNotYetRecognized_fbb5a473-d0ab-4bae-bfee-dc34d4f855cf" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AllocatedShareBasedCompensationExpense_d54e22c2-e8b7-4f4a-afb3-b0cfe5d8195a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AllocatedShareBasedCompensationExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_c6c4032f-45cf-4a6c-ab6a-39b8f60f10f1" xlink:to="loc_us-gaap_AllocatedShareBasedCompensationExpense_d54e22c2-e8b7-4f4a-afb3-b0cfe5d8195a" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized_39778eef-6498-49c0-8f29-b2d69d5d941e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_c6c4032f-45cf-4a6c-ab6a-39b8f60f10f1" xlink:to="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized_39778eef-6498-49c0-8f29-b2d69d5d941e" xlink:type="arc" order="4"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.thefirst.com/role/StockBasedCompensationScheduleofRestrictedStockGrantedDetails" xlink:type="simple" xlink:href="fnlc-20260331.xsd#StockBasedCompensationScheduleofRestrictedStockGrantedDetails"/>
  <link:definitionLink xlink:role="http://www.thefirst.com/role/StockBasedCompensationScheduleofRestrictedStockGrantedDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_0771e82d-1edb-43c8-9b48-cdfdd327fb86" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_838caae7-67ce-4e82-a9b5-a59ae08c3be6" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_0771e82d-1edb-43c8-9b48-cdfdd327fb86" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_838caae7-67ce-4e82-a9b5-a59ae08c3be6" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameAxis_93cf2000-fb0a-4155-99d6-ce00b0a00dc3" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PlanNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_838caae7-67ce-4e82-a9b5-a59ae08c3be6" xlink:to="loc_us-gaap_PlanNameAxis_93cf2000-fb0a-4155-99d6-ce00b0a00dc3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameDomain_93cf2000-fb0a-4155-99d6-ce00b0a00dc3_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PlanNameAxis_93cf2000-fb0a-4155-99d6-ce00b0a00dc3" xlink:to="loc_us-gaap_PlanNameDomain_93cf2000-fb0a-4155-99d6-ce00b0a00dc3_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameDomain_93443043-1cfa-4920-9a6e-3b48276d0db9" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PlanNameAxis_93cf2000-fb0a-4155-99d6-ce00b0a00dc3" xlink:to="loc_us-gaap_PlanNameDomain_93443043-1cfa-4920-9a6e-3b48276d0db9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_fnlc_A2020EquityIncentivePlanMember_019d72e4-b00c-798a-93cb-012ab72a23cb" xlink:href="fnlc-20260331.xsd#fnlc_A2020EquityIncentivePlanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PlanNameDomain_93443043-1cfa-4920-9a6e-3b48276d0db9" xlink:to="loc_fnlc_A2020EquityIncentivePlanMember_019d72e4-b00c-798a-93cb-012ab72a23cb" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_9185b87b-9ee1-4e00-852a-08a57950e04d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_838caae7-67ce-4e82-a9b5-a59ae08c3be6" xlink:to="loc_us-gaap_AwardTypeAxis_9185b87b-9ee1-4e00-852a-08a57950e04d" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_9185b87b-9ee1-4e00-852a-08a57950e04d_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_9185b87b-9ee1-4e00-852a-08a57950e04d" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_9185b87b-9ee1-4e00-852a-08a57950e04d_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_1a688e4c-a57f-4af6-b5f6-f2a05780faa3" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_9185b87b-9ee1-4e00-852a-08a57950e04d" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_1a688e4c-a57f-4af6-b5f6-f2a05780faa3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockMember_a5359808-fe4c-498b-a896-7161ca4f5c88" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RestrictedStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_1a688e4c-a57f-4af6-b5f6-f2a05780faa3" xlink:to="loc_us-gaap_RestrictedStockMember_a5359808-fe4c-498b-a896-7161ca4f5c88" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardDateAxis_321a0bea-96a5-4b22-83cc-e551aa43e338" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AwardDateAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_838caae7-67ce-4e82-a9b5-a59ae08c3be6" xlink:to="loc_us-gaap_AwardDateAxis_321a0bea-96a5-4b22-83cc-e551aa43e338" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardDateDomain_321a0bea-96a5-4b22-83cc-e551aa43e338_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AwardDateDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardDateAxis_321a0bea-96a5-4b22-83cc-e551aa43e338" xlink:to="loc_us-gaap_AwardDateDomain_321a0bea-96a5-4b22-83cc-e551aa43e338_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardDateDomain_0f3666fa-c886-43b0-8b87-b488c937d127" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AwardDateDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardDateAxis_321a0bea-96a5-4b22-83cc-e551aa43e338" xlink:to="loc_us-gaap_AwardDateDomain_0f3666fa-c886-43b0-8b87-b488c937d127" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_fnlc_YearAwarded2024Member_198c0d5d-d230-449a-bb97-ef3502741302" xlink:href="fnlc-20260331.xsd#fnlc_YearAwarded2024Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AwardDateDomain_0f3666fa-c886-43b0-8b87-b488c937d127" xlink:to="loc_fnlc_YearAwarded2024Member_198c0d5d-d230-449a-bb97-ef3502741302" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_fnlc_YearAwarded2025Member_3b7b5af3-9eb9-40be-b74f-0bb47eeaef5e" xlink:href="fnlc-20260331.xsd#fnlc_YearAwarded2025Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AwardDateDomain_0f3666fa-c886-43b0-8b87-b488c937d127" xlink:to="loc_fnlc_YearAwarded2025Member_3b7b5af3-9eb9-40be-b74f-0bb47eeaef5e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_fnlc_YearAwarded2026Member_019d298d-5f40-7cd6-badc-6ba3e90bd212" xlink:href="fnlc-20260331.xsd#fnlc_YearAwarded2026Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AwardDateDomain_0f3666fa-c886-43b0-8b87-b488c937d127" xlink:to="loc_fnlc_YearAwarded2026Member_019d298d-5f40-7cd6-badc-6ba3e90bd212" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VestingAxis_7627899c-380c-41fb-8eda-acbb51b14d1a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_VestingAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_838caae7-67ce-4e82-a9b5-a59ae08c3be6" xlink:to="loc_us-gaap_VestingAxis_7627899c-380c-41fb-8eda-acbb51b14d1a" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VestingDomain_7627899c-380c-41fb-8eda-acbb51b14d1a_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_VestingDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_VestingAxis_7627899c-380c-41fb-8eda-acbb51b14d1a" xlink:to="loc_us-gaap_VestingDomain_7627899c-380c-41fb-8eda-acbb51b14d1a_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VestingDomain_4e352daa-233b-452a-8ce7-45478aab81c9" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_VestingDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_VestingAxis_7627899c-380c-41fb-8eda-acbb51b14d1a" xlink:to="loc_us-gaap_VestingDomain_4e352daa-233b-452a-8ce7-45478aab81c9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_fnlc_ThreeYearsMember_8981ae1a-df5a-48b6-b02a-a0583ffaaa1a" xlink:href="fnlc-20260331.xsd#fnlc_ThreeYearsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VestingDomain_4e352daa-233b-452a-8ce7-45478aab81c9" xlink:to="loc_fnlc_ThreeYearsMember_8981ae1a-df5a-48b6-b02a-a0583ffaaa1a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_fnlc_OneYearMember_5fe65fbc-dee6-461f-bdcf-c30120af1b9b" xlink:href="fnlc-20260331.xsd#fnlc_OneYearMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VestingDomain_4e352daa-233b-452a-8ce7-45478aab81c9" xlink:to="loc_fnlc_OneYearMember_5fe65fbc-dee6-461f-bdcf-c30120af1b9b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_fnlc_SixMonthsMember_019d2a38-e839-7a04-92dc-6fed09cc2f18" xlink:href="fnlc-20260331.xsd#fnlc_SixMonthsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VestingDomain_4e352daa-233b-452a-8ce7-45478aab81c9" xlink:to="loc_fnlc_SixMonthsMember_019d2a38-e839-7a04-92dc-6fed09cc2f18" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_fnlc_TwoMonthsTwelveDaysMember_019d2a3a-6ffd-7435-ba5c-39598c9cec31" xlink:href="fnlc-20260331.xsd#fnlc_TwoMonthsTwelveDaysMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VestingDomain_4e352daa-233b-452a-8ce7-45478aab81c9" xlink:to="loc_fnlc_TwoMonthsTwelveDaysMember_019d2a3a-6ffd-7435-ba5c-39598c9cec31" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1_a730bcf9-1782-47db-adc9-9312974bd6d4" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_0771e82d-1edb-43c8-9b48-cdfdd327fb86" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1_a730bcf9-1782-47db-adc9-9312974bd6d4" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_c5380f7d-3207-43fb-b119-24becde30f75" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_0771e82d-1edb-43c8-9b48-cdfdd327fb86" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_c5380f7d-3207-43fb-b119-24becde30f75" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1_dc21f3e6-e0df-43af-bc32-56b2caccc0a3" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_0771e82d-1edb-43c8-9b48-cdfdd327fb86" xlink:to="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1_dc21f3e6-e0df-43af-bc32-56b2caccc0a3" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.thefirst.com/role/CommonStockDetails" xlink:type="simple" xlink:href="fnlc-20260331.xsd#CommonStockDetails"/>
  <link:definitionLink xlink:role="http://www.thefirst.com/role/CommonStockDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockLineItems_7d52171e-0611-4014-bfbe-95a8c4a911d4" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ClassOfStockLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfStockByClassTable_d20b06d6-88d1-4175-a343-7c31c0ce6673" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfStockByClassTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ClassOfStockLineItems_7d52171e-0611-4014-bfbe-95a8c4a911d4" xlink:to="loc_us-gaap_ScheduleOfStockByClassTable_d20b06d6-88d1-4175-a343-7c31c0ce6673" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ShareRepurchaseProgramAxis_d1175841-747e-402c-96a6-a57224a2d805" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ShareRepurchaseProgramAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfStockByClassTable_d20b06d6-88d1-4175-a343-7c31c0ce6673" xlink:to="loc_srt_ShareRepurchaseProgramAxis_d1175841-747e-402c-96a6-a57224a2d805" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ShareRepurchaseProgramDomain_d1175841-747e-402c-96a6-a57224a2d805_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ShareRepurchaseProgramDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ShareRepurchaseProgramAxis_d1175841-747e-402c-96a6-a57224a2d805" xlink:to="loc_srt_ShareRepurchaseProgramDomain_d1175841-747e-402c-96a6-a57224a2d805_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ShareRepurchaseProgramDomain_cf60b005-1119-44eb-838a-5e7279541ad3" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ShareRepurchaseProgramDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ShareRepurchaseProgramAxis_d1175841-747e-402c-96a6-a57224a2d805" xlink:to="loc_srt_ShareRepurchaseProgramDomain_cf60b005-1119-44eb-838a-5e7279541ad3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_fnlc_CapitalPurchaseProgramMember_1cd4f243-3b75-4b14-bc24-9264d5c48b9c" xlink:href="fnlc-20260331.xsd#fnlc_CapitalPurchaseProgramMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ShareRepurchaseProgramDomain_cf60b005-1119-44eb-838a-5e7279541ad3" xlink:to="loc_fnlc_CapitalPurchaseProgramMember_1cd4f243-3b75-4b14-bc24-9264d5c48b9c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodValueNewIssues_df33e6c4-c734-4edd-8cfd-dcb7d289ed61" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockIssuedDuringPeriodValueNewIssues"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_7d52171e-0611-4014-bfbe-95a8c4a911d4" xlink:to="loc_us-gaap_StockIssuedDuringPeriodValueNewIssues_df33e6c4-c734-4edd-8cfd-dcb7d289ed61" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.thefirst.com/role/OtherComprehensiveIncomeLossSummaryofUnrealizedGainsandLossesonAvailableforSaleSecuritiesDetails" xlink:type="simple" xlink:href="fnlc-20260331.xsd#OtherComprehensiveIncomeLossSummaryofUnrealizedGainsandLossesonAvailableforSaleSecuritiesDetails"/>
  <link:definitionLink xlink:role="http://www.thefirst.com/role/OtherComprehensiveIncomeLossSummaryofUnrealizedGainsandLossesonAvailableforSaleSecuritiesDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossLineItems_4613cbc6-d340-4921-89f6-801aac0bbd99" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeLossLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossTable_70a8518d-246d-4ad1-81e6-d2f3b68b24b3" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeLossTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossLineItems_4613cbc6-d340-4921-89f6-801aac0bbd99" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossTable_70a8518d-246d-4ad1-81e6-d2f3b68b24b3" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_ad35e109-5887-4040-93bd-7e4e1b20d65b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementEquityComponentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossTable_70a8518d-246d-4ad1-81e6-d2f3b68b24b3" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_ad35e109-5887-4040-93bd-7e4e1b20d65b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_ad35e109-5887-4040-93bd-7e4e1b20d65b_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_ad35e109-5887-4040-93bd-7e4e1b20d65b" xlink:to="loc_us-gaap_EquityComponentDomain_ad35e109-5887-4040-93bd-7e4e1b20d65b_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_e015a661-407a-4f8e-b51d-fe227fa79025" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_ad35e109-5887-4040-93bd-7e4e1b20d65b" xlink:to="loc_us-gaap_EquityComponentDomain_e015a661-407a-4f8e-b51d-fe227fa79025" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedNetUnrealizedInvestmentGainLossMember_6da931da-b01e-4b54-9828-6361f4812f8e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AccumulatedNetUnrealizedInvestmentGainLossMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_e015a661-407a-4f8e-b51d-fe227fa79025" xlink:to="loc_us-gaap_AccumulatedNetUnrealizedInvestmentGainLossMember_6da931da-b01e-4b54-9828-6361f4812f8e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AOCIAttributableToParentNetOfTaxRollForward_adc35356-da99-49c0-a22a-b364a921381f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AOCIAttributableToParentNetOfTaxRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossLineItems_4613cbc6-d340-4921-89f6-801aac0bbd99" xlink:to="loc_us-gaap_AOCIAttributableToParentNetOfTaxRollForward_adc35356-da99-49c0-a22a-b364a921381f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquity_43859114-a628-4198-bf18-85063c17cab8" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockholdersEquity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AOCIAttributableToParentNetOfTaxRollForward_adc35356-da99-49c0-a22a-b364a921381f" xlink:to="loc_us-gaap_StockholdersEquity_43859114-a628-4198-bf18-85063c17cab8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OciBeforeReclassificationsBeforeTaxAttributableToParent_152a5b5f-4734-45d7-a7d4-63a8d54ad5ad" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OciBeforeReclassificationsBeforeTaxAttributableToParent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AOCIAttributableToParentNetOfTaxRollForward_adc35356-da99-49c0-a22a-b364a921381f" xlink:to="loc_us-gaap_OciBeforeReclassificationsBeforeTaxAttributableToParent_152a5b5f-4734-45d7-a7d4-63a8d54ad5ad" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ReclassificationFromAociCurrentPeriodBeforeTaxAttributableToParent_019d84af-7919-7e90-be05-875d1d669533" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ReclassificationFromAociCurrentPeriodBeforeTaxAttributableToParent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AOCIAttributableToParentNetOfTaxRollForward_adc35356-da99-49c0-a22a-b364a921381f" xlink:to="loc_us-gaap_ReclassificationFromAociCurrentPeriodBeforeTaxAttributableToParent_019d84af-7919-7e90-be05-875d1d669533" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossTaxPortionAttributableToParent1_70f4d267-c711-42b7-895c-f849b87cd0a7" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherComprehensiveIncomeLossTaxPortionAttributableToParent1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AOCIAttributableToParentNetOfTaxRollForward_adc35356-da99-49c0-a22a-b364a921381f" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossTaxPortionAttributableToParent1_70f4d267-c711-42b7-895c-f849b87cd0a7" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent_ae8ee3a6-1c36-49f4-8a81-1cfa12ffe8d7" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AOCIAttributableToParentNetOfTaxRollForward_adc35356-da99-49c0-a22a-b364a921381f" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent_ae8ee3a6-1c36-49f4-8a81-1cfa12ffe8d7" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquity_2ee86ca1-4868-4817-960b-621a29a6fb58" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockholdersEquity"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.thefirst.com/role/OtherComprehensiveIncomeLossSummaryofTransferofAFSSecuritiestoHTMDetails" xlink:type="simple" xlink:href="fnlc-20260331.xsd#OtherComprehensiveIncomeLossSummaryofTransferofAFSSecuritiestoHTMDetails"/>
  <link:definitionLink xlink:role="http://www.thefirst.com/role/OtherComprehensiveIncomeLossSummaryofTransferofAFSSecuritiestoHTMDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossLineItems_1c92eae2-516a-4c73-bf25-593a700abec1" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeLossLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossTable_93aea833-2160-4bb8-892f-27f1d4e181b5" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeLossTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossLineItems_1c92eae2-516a-4c73-bf25-593a700abec1" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossTable_93aea833-2160-4bb8-892f-27f1d4e181b5" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_a8d29e12-847d-492c-97f3-bf56058b0d36" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementEquityComponentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossTable_93aea833-2160-4bb8-892f-27f1d4e181b5" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_a8d29e12-847d-492c-97f3-bf56058b0d36" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_a8d29e12-847d-492c-97f3-bf56058b0d36_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_a8d29e12-847d-492c-97f3-bf56058b0d36" xlink:to="loc_us-gaap_EquityComponentDomain_a8d29e12-847d-492c-97f3-bf56058b0d36_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_2e80c3ef-fbeb-41f2-ace1-54e55a971fbb" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_a8d29e12-847d-492c-97f3-bf56058b0d36" xlink:to="loc_us-gaap_EquityComponentDomain_2e80c3ef-fbeb-41f2-ace1-54e55a971fbb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_fnlc_AccumulatedNetGainLossonSecuritiesTransferredfromAvailableforSaletoHeldtoMaturityMember_b6df173a-c741-4c2c-a93d-653875c934e3" xlink:href="fnlc-20260331.xsd#fnlc_AccumulatedNetGainLossonSecuritiesTransferredfromAvailableforSaletoHeldtoMaturityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_2e80c3ef-fbeb-41f2-ace1-54e55a971fbb" xlink:to="loc_fnlc_AccumulatedNetGainLossonSecuritiesTransferredfromAvailableforSaletoHeldtoMaturityMember_b6df173a-c741-4c2c-a93d-653875c934e3" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AOCIAttributableToParentNetOfTaxRollForward_cdf9e7fb-6f2f-4cd7-b54c-4dfa88012872" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AOCIAttributableToParentNetOfTaxRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossLineItems_1c92eae2-516a-4c73-bf25-593a700abec1" xlink:to="loc_us-gaap_AOCIAttributableToParentNetOfTaxRollForward_cdf9e7fb-6f2f-4cd7-b54c-4dfa88012872" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquity_32cc23ed-9a85-413a-b3c4-ff8f6909f0e4" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockholdersEquity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AOCIAttributableToParentNetOfTaxRollForward_cdf9e7fb-6f2f-4cd7-b54c-4dfa88012872" xlink:to="loc_us-gaap_StockholdersEquity_32cc23ed-9a85-413a-b3c4-ff8f6909f0e4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ReclassificationFromAociCurrentPeriodBeforeTaxAttributableToParent_56abb686-2607-49cc-992e-0537b9bd86c3" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ReclassificationFromAociCurrentPeriodBeforeTaxAttributableToParent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AOCIAttributableToParentNetOfTaxRollForward_cdf9e7fb-6f2f-4cd7-b54c-4dfa88012872" xlink:to="loc_us-gaap_ReclassificationFromAociCurrentPeriodBeforeTaxAttributableToParent_56abb686-2607-49cc-992e-0537b9bd86c3" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossTaxPortionAttributableToParent1_eb58007b-e245-4c3e-b830-380ec090dbe1" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherComprehensiveIncomeLossTaxPortionAttributableToParent1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AOCIAttributableToParentNetOfTaxRollForward_cdf9e7fb-6f2f-4cd7-b54c-4dfa88012872" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossTaxPortionAttributableToParent1_eb58007b-e245-4c3e-b830-380ec090dbe1" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent_3ced59c0-f0f1-4d7d-9200-58130fb4a644" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AOCIAttributableToParentNetOfTaxRollForward_cdf9e7fb-6f2f-4cd7-b54c-4dfa88012872" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent_3ced59c0-f0f1-4d7d-9200-58130fb4a644" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquity_9d457e3b-2671-4f1d-b531-19c07a40b6aa" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockholdersEquity"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.thefirst.com/role/OtherComprehensiveIncomeLossSummaryofDerivativeFinancialInstrumentsDetails" xlink:type="simple" xlink:href="fnlc-20260331.xsd#OtherComprehensiveIncomeLossSummaryofDerivativeFinancialInstrumentsDetails"/>
  <link:definitionLink xlink:role="http://www.thefirst.com/role/OtherComprehensiveIncomeLossSummaryofDerivativeFinancialInstrumentsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossLineItems_796110d5-e477-4524-b2df-019c7ce386ff" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeLossLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossTable_4a6c1517-7f3d-4133-b587-ac0f0502327b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeLossTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossLineItems_796110d5-e477-4524-b2df-019c7ce386ff" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossTable_4a6c1517-7f3d-4133-b587-ac0f0502327b" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_01dae647-8cda-4bfb-8571-798bdcecb399" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementEquityComponentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossTable_4a6c1517-7f3d-4133-b587-ac0f0502327b" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_01dae647-8cda-4bfb-8571-798bdcecb399" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_01dae647-8cda-4bfb-8571-798bdcecb399_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_01dae647-8cda-4bfb-8571-798bdcecb399" xlink:to="loc_us-gaap_EquityComponentDomain_01dae647-8cda-4bfb-8571-798bdcecb399_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_7b9d26d8-c1bd-4cf4-b413-49862fae40ad" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_01dae647-8cda-4bfb-8571-798bdcecb399" xlink:to="loc_us-gaap_EquityComponentDomain_7b9d26d8-c1bd-4cf4-b413-49862fae40ad" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedGainLossNetCashFlowHedgeParentMember_a5f8bb11-c777-41a0-806c-e11ea1b2d411" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AccumulatedGainLossNetCashFlowHedgeParentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_7b9d26d8-c1bd-4cf4-b413-49862fae40ad" xlink:to="loc_us-gaap_AccumulatedGainLossNetCashFlowHedgeParentMember_a5f8bb11-c777-41a0-806c-e11ea1b2d411" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AOCIAttributableToParentNetOfTaxRollForward_09b4cc2b-e7fa-48bd-9af0-1b2a0484b4ab" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AOCIAttributableToParentNetOfTaxRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossLineItems_796110d5-e477-4524-b2df-019c7ce386ff" xlink:to="loc_us-gaap_AOCIAttributableToParentNetOfTaxRollForward_09b4cc2b-e7fa-48bd-9af0-1b2a0484b4ab" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquity_76a86f2f-253b-45b3-a1ef-8b97961cd28e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockholdersEquity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AOCIAttributableToParentNetOfTaxRollForward_09b4cc2b-e7fa-48bd-9af0-1b2a0484b4ab" xlink:to="loc_us-gaap_StockholdersEquity_76a86f2f-253b-45b3-a1ef-8b97961cd28e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OciBeforeReclassificationsBeforeTaxAttributableToParent_4a7694d1-c2cd-4b01-95de-28eaac3a6042" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OciBeforeReclassificationsBeforeTaxAttributableToParent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AOCIAttributableToParentNetOfTaxRollForward_09b4cc2b-e7fa-48bd-9af0-1b2a0484b4ab" xlink:to="loc_us-gaap_OciBeforeReclassificationsBeforeTaxAttributableToParent_4a7694d1-c2cd-4b01-95de-28eaac3a6042" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossTaxPortionAttributableToParent1_aaa30bcd-bb87-4343-b378-939abb2aa05d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherComprehensiveIncomeLossTaxPortionAttributableToParent1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AOCIAttributableToParentNetOfTaxRollForward_09b4cc2b-e7fa-48bd-9af0-1b2a0484b4ab" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossTaxPortionAttributableToParent1_aaa30bcd-bb87-4343-b378-939abb2aa05d" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent_d4c4101e-8d25-410d-9dee-1b3420581abb" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AOCIAttributableToParentNetOfTaxRollForward_09b4cc2b-e7fa-48bd-9af0-1b2a0484b4ab" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent_d4c4101e-8d25-410d-9dee-1b3420581abb" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquity_b188b68b-af0c-43b6-aa37-9acc5989294c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockholdersEquity"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.thefirst.com/role/FinancialDerivativeInstrumentsDetails" xlink:type="simple" xlink:href="fnlc-20260331.xsd#FinancialDerivativeInstrumentsDetails"/>
  <link:definitionLink xlink:role="http://www.thefirst.com/role/FinancialDerivativeInstrumentsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeLineItems_8afd99e1-2075-477f-92c1-f23af80e7b7d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeTable_686e47a6-bbfd-4a5a-9892-3e5841a65049" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DerivativeLineItems_8afd99e1-2075-477f-92c1-f23af80e7b7d" xlink:to="loc_us-gaap_DerivativeTable_686e47a6-bbfd-4a5a-9892-3e5841a65049" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis_4a4e7f49-0756-4b55-b9d4-2c5d47da3c35" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeTable_686e47a6-bbfd-4a5a-9892-3e5841a65049" xlink:to="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis_4a4e7f49-0756-4b55-b9d4-2c5d47da3c35" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingRelationshipDomain_4a4e7f49-0756-4b55-b9d4-2c5d47da3c35_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_HedgingRelationshipDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis_4a4e7f49-0756-4b55-b9d4-2c5d47da3c35" xlink:to="loc_us-gaap_HedgingRelationshipDomain_4a4e7f49-0756-4b55-b9d4-2c5d47da3c35_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingRelationshipDomain_05a01f51-6414-427f-818d-893d903f86dc" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_HedgingRelationshipDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis_4a4e7f49-0756-4b55-b9d4-2c5d47da3c35" xlink:to="loc_us-gaap_HedgingRelationshipDomain_05a01f51-6414-427f-818d-893d903f86dc" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashFlowHedgingMember_63d06644-a934-4eab-8f0c-223d03986299" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CashFlowHedgingMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_HedgingRelationshipDomain_05a01f51-6414-427f-818d-893d903f86dc" xlink:to="loc_us-gaap_CashFlowHedgingMember_63d06644-a934-4eab-8f0c-223d03986299" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueHedgingMember_544a9ce8-80e3-404d-8a62-5dbfc3fd0b68" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueHedgingMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_HedgingRelationshipDomain_05a01f51-6414-427f-818d-893d903f86dc" xlink:to="loc_us-gaap_FairValueHedgingMember_544a9ce8-80e3-404d-8a62-5dbfc3fd0b68" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingDesignationAxis_f2a25fc2-c336-45f8-8e69-7820b957cd01" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_HedgingDesignationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeTable_686e47a6-bbfd-4a5a-9892-3e5841a65049" xlink:to="loc_us-gaap_HedgingDesignationAxis_f2a25fc2-c336-45f8-8e69-7820b957cd01" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingDesignationDomain_f2a25fc2-c336-45f8-8e69-7820b957cd01_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_HedgingDesignationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_HedgingDesignationAxis_f2a25fc2-c336-45f8-8e69-7820b957cd01" xlink:to="loc_us-gaap_HedgingDesignationDomain_f2a25fc2-c336-45f8-8e69-7820b957cd01_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingDesignationDomain_5625f103-d8d8-48a6-9b94-eb747294b3f6" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_HedgingDesignationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_HedgingDesignationAxis_f2a25fc2-c336-45f8-8e69-7820b957cd01" xlink:to="loc_us-gaap_HedgingDesignationDomain_5625f103-d8d8-48a6-9b94-eb747294b3f6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DesignatedAsHedgingInstrumentMember_da41d940-785c-42ec-99de-43ff88f6bea8" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DesignatedAsHedgingInstrumentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_HedgingDesignationDomain_5625f103-d8d8-48a6-9b94-eb747294b3f6" xlink:to="loc_us-gaap_DesignatedAsHedgingInstrumentMember_da41d940-785c-42ec-99de-43ff88f6bea8" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NondesignatedMember_108a1818-2bf6-40e7-93aa-a0763fefa5d6" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_NondesignatedMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_HedgingDesignationDomain_5625f103-d8d8-48a6-9b94-eb747294b3f6" xlink:to="loc_us-gaap_NondesignatedMember_108a1818-2bf6-40e7-93aa-a0763fefa5d6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentRiskAxis_0f2e01a4-e9bc-47df-b273-9e4a77a9dc99" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeInstrumentRiskAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeTable_686e47a6-bbfd-4a5a-9892-3e5841a65049" xlink:to="loc_us-gaap_DerivativeInstrumentRiskAxis_0f2e01a4-e9bc-47df-b273-9e4a77a9dc99" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_0f2e01a4-e9bc-47df-b273-9e4a77a9dc99_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_0f2e01a4-e9bc-47df-b273-9e4a77a9dc99" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_0f2e01a4-e9bc-47df-b273-9e4a77a9dc99_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_26634c91-1edf-4213-8c5c-bee2de5669e8" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_0f2e01a4-e9bc-47df-b273-9e4a77a9dc99" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_26634c91-1edf-4213-8c5c-bee2de5669e8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestRateSwapMember_8c9e3336-1478-4765-83eb-9116a797e3ef" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_InterestRateSwapMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_26634c91-1edf-4213-8c5c-bee2de5669e8" xlink:to="loc_us-gaap_InterestRateSwapMember_8c9e3336-1478-4765-83eb-9116a797e3ef" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_fnlc_InterestRateSwapJanuary012026Member_a9e234b3-a324-43d5-804c-5c99d89a41cb" xlink:href="fnlc-20260331.xsd#fnlc_InterestRateSwapJanuary012026Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InterestRateSwapMember_8c9e3336-1478-4765-83eb-9116a797e3ef" xlink:to="loc_fnlc_InterestRateSwapJanuary012026Member_a9e234b3-a324-43d5-804c-5c99d89a41cb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_fnlc_InterestRateSwapMarch012026Member_55f7c7ca-ec51-4d1d-acff-98d4c053d721" xlink:href="fnlc-20260331.xsd#fnlc_InterestRateSwapMarch012026Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InterestRateSwapMember_8c9e3336-1478-4765-83eb-9116a797e3ef" xlink:to="loc_fnlc_InterestRateSwapMarch012026Member_55f7c7ca-ec51-4d1d-acff-98d4c053d721" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_fnlc_InterestRateSwapMarch012027Member_ac9c3553-a84d-4de1-8e95-9bfa158a4074" xlink:href="fnlc-20260331.xsd#fnlc_InterestRateSwapMarch012027Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InterestRateSwapMember_8c9e3336-1478-4765-83eb-9116a797e3ef" xlink:to="loc_fnlc_InterestRateSwapMarch012027Member_ac9c3553-a84d-4de1-8e95-9bfa158a4074" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_fnlc_InterestRateSwapMarch012028Member_17b1909a-7773-4d0e-9156-e25f9d6f5fa4" xlink:href="fnlc-20260331.xsd#fnlc_InterestRateSwapMarch012028Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InterestRateSwapMember_8c9e3336-1478-4765-83eb-9116a797e3ef" xlink:to="loc_fnlc_InterestRateSwapMarch012028Member_17b1909a-7773-4d0e-9156-e25f9d6f5fa4" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_fnlc_InterestRateSwapAugust012025Member_1df2c482-37c5-4cfb-aa09-e2196b448a95" xlink:href="fnlc-20260331.xsd#fnlc_InterestRateSwapAugust012025Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InterestRateSwapMember_8c9e3336-1478-4765-83eb-9116a797e3ef" xlink:to="loc_fnlc_InterestRateSwapAugust012025Member_1df2c482-37c5-4cfb-aa09-e2196b448a95" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestRateCapMember_435d612c-7acc-4916-9dc3-1d27bb07de38" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_InterestRateCapMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_26634c91-1edf-4213-8c5c-bee2de5669e8" xlink:to="loc_us-gaap_InterestRateCapMember_435d612c-7acc-4916-9dc3-1d27bb07de38" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_fnlc_InterestRateCapJuly012028At4.050Member_dc48ea23-6d62-4a16-8208-4a424071e67c" xlink:href="fnlc-20260331.xsd#fnlc_InterestRateCapJuly012028At4.050Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InterestRateCapMember_435d612c-7acc-4916-9dc3-1d27bb07de38" xlink:to="loc_fnlc_InterestRateCapJuly012028At4.050Member_dc48ea23-6d62-4a16-8208-4a424071e67c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_fnlc_InterestRateCapJuly012028At4.550Member_4e511c40-381a-432b-aa35-9b30650fe58e" xlink:href="fnlc-20260331.xsd#fnlc_InterestRateCapJuly012028At4.550Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InterestRateCapMember_435d612c-7acc-4916-9dc3-1d27bb07de38" xlink:to="loc_fnlc_InterestRateCapJuly012028At4.550Member_4e511c40-381a-432b-aa35-9b30650fe58e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_fnlc_InterestRateCapMarch012029At3.750Member_019d84b3-4957-7bf6-981f-458ee3039fda" xlink:href="fnlc-20260331.xsd#fnlc_InterestRateCapMarch012029At3.750Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InterestRateCapMember_435d612c-7acc-4916-9dc3-1d27bb07de38" xlink:to="loc_fnlc_InterestRateCapMarch012029At3.750Member_019d84b3-4957-7bf6-981f-458ee3039fda" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_fnlc_InterestRateCapMarch012030At4.250Member_019d84b4-0612-76f9-bd42-d9317c5e37a2" xlink:href="fnlc-20260331.xsd#fnlc_InterestRateCapMarch012030At4.250Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InterestRateCapMember_435d612c-7acc-4916-9dc3-1d27bb07de38" xlink:to="loc_fnlc_InterestRateCapMarch012030At4.250Member_019d84b4-0612-76f9-bd42-d9317c5e37a2" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_fnlc_CustomerLoanInterestSwapMember_1e111cee-6928-47ec-b7f3-745b0b41e1a4" xlink:href="fnlc-20260331.xsd#fnlc_CustomerLoanInterestSwapMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_26634c91-1edf-4213-8c5c-bee2de5669e8" xlink:to="loc_fnlc_CustomerLoanInterestSwapMember_1e111cee-6928-47ec-b7f3-745b0b41e1a4" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BalanceSheetLocationAxis_494fc00d-957f-4dd2-ad13-13a33314bce8" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BalanceSheetLocationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeTable_686e47a6-bbfd-4a5a-9892-3e5841a65049" xlink:to="loc_us-gaap_BalanceSheetLocationAxis_494fc00d-957f-4dd2-ad13-13a33314bce8" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BalanceSheetLocationDomain_494fc00d-957f-4dd2-ad13-13a33314bce8_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BalanceSheetLocationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_BalanceSheetLocationAxis_494fc00d-957f-4dd2-ad13-13a33314bce8" xlink:to="loc_us-gaap_BalanceSheetLocationDomain_494fc00d-957f-4dd2-ad13-13a33314bce8_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BalanceSheetLocationDomain_a11617bb-1dc3-4de0-8362-eb91cc82ccc6" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BalanceSheetLocationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_BalanceSheetLocationAxis_494fc00d-957f-4dd2-ad13-13a33314bce8" xlink:to="loc_us-gaap_BalanceSheetLocationDomain_a11617bb-1dc3-4de0-8362-eb91cc82ccc6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherAssetsMember_e2398427-7653-436d-ab7e-6d8110fb75d3" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherAssetsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BalanceSheetLocationDomain_a11617bb-1dc3-4de0-8362-eb91cc82ccc6" xlink:to="loc_us-gaap_OtherAssetsMember_e2398427-7653-436d-ab7e-6d8110fb75d3" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherLiabilitiesMember_dc7f30e8-d6c0-41fc-a15e-fe25bb2f5ef7" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherLiabilitiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BalanceSheetLocationDomain_a11617bb-1dc3-4de0-8362-eb91cc82ccc6" xlink:to="loc_us-gaap_OtherLiabilitiesMember_dc7f30e8-d6c0-41fc-a15e-fe25bb2f5ef7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_fnlc_DerivativeSwapTypeAxis_465e9efa-3ff9-4468-aeae-4ca8402208c8" xlink:href="fnlc-20260331.xsd#fnlc_DerivativeSwapTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeTable_686e47a6-bbfd-4a5a-9892-3e5841a65049" xlink:to="loc_fnlc_DerivativeSwapTypeAxis_465e9efa-3ff9-4468-aeae-4ca8402208c8" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_fnlc_DerivativeSwapTypeDomain_465e9efa-3ff9-4468-aeae-4ca8402208c8_default" xlink:href="fnlc-20260331.xsd#fnlc_DerivativeSwapTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_fnlc_DerivativeSwapTypeAxis_465e9efa-3ff9-4468-aeae-4ca8402208c8" xlink:to="loc_fnlc_DerivativeSwapTypeDomain_465e9efa-3ff9-4468-aeae-4ca8402208c8_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_fnlc_DerivativeSwapTypeDomain_cf607d0f-dc2f-49df-acd1-d069da4bf0e7" xlink:href="fnlc-20260331.xsd#fnlc_DerivativeSwapTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_fnlc_DerivativeSwapTypeAxis_465e9efa-3ff9-4468-aeae-4ca8402208c8" xlink:to="loc_fnlc_DerivativeSwapTypeDomain_cf607d0f-dc2f-49df-acd1-d069da4bf0e7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_fnlc_PayFixedReceiveVariableMember_47daf81b-78fa-461e-a743-b9414f7bd5de" xlink:href="fnlc-20260331.xsd#fnlc_PayFixedReceiveVariableMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_fnlc_DerivativeSwapTypeDomain_cf607d0f-dc2f-49df-acd1-d069da4bf0e7" xlink:to="loc_fnlc_PayFixedReceiveVariableMember_47daf81b-78fa-461e-a743-b9414f7bd5de" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_fnlc_ReceiveFixedPayVariableMember_0995cd78-04c5-4991-859b-245aa656b22e" xlink:href="fnlc-20260331.xsd#fnlc_ReceiveFixedPayVariableMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_fnlc_DerivativeSwapTypeDomain_cf607d0f-dc2f-49df-acd1-d069da4bf0e7" xlink:to="loc_fnlc_ReceiveFixedPayVariableMember_0995cd78-04c5-4991-859b-245aa656b22e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeFixedInterestRate_8eea194a-0ab0-4b79-b910-f9ed1a308afa" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeFixedInterestRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_8afd99e1-2075-477f-92c1-f23af80e7b7d" xlink:to="loc_us-gaap_DerivativeFixedInterestRate_8eea194a-0ab0-4b79-b910-f9ed1a308afa" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeNotionalAmount_a9f43b7f-7e2f-4a8f-a9b8-9c6272cd3e31" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeNotionalAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_8afd99e1-2075-477f-92c1-f23af80e7b7d" xlink:to="loc_us-gaap_DerivativeNotionalAmount_a9f43b7f-7e2f-4a8f-a9b8-9c6272cd3e31" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeFairValueOfDerivativeNet_d5963ce7-5c9a-4af1-b23f-b1cb9c3f6a32" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeFairValueOfDerivativeNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_8afd99e1-2075-477f-92c1-f23af80e7b7d" xlink:to="loc_us-gaap_DerivativeFairValueOfDerivativeNet_d5963ce7-5c9a-4af1-b23f-b1cb9c3f6a32" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeNumberOfInstrumentsHeld_46a53219-8a2c-42bd-af27-43d0533c2d4e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeNumberOfInstrumentsHeld"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_8afd99e1-2075-477f-92c1-f23af80e7b7d" xlink:to="loc_us-gaap_DerivativeNumberOfInstrumentsHeld_46a53219-8a2c-42bd-af27-43d0533c2d4e" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeCollateralObligationToReturnCash_a06225c7-20f4-4bb5-86eb-c209b2bad3b0" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeCollateralObligationToReturnCash"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_8afd99e1-2075-477f-92c1-f23af80e7b7d" xlink:to="loc_us-gaap_DerivativeCollateralObligationToReturnCash_a06225c7-20f4-4bb5-86eb-c209b2bad3b0" xlink:type="arc" order="4"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.thefirst.com/role/FairValueAssetsandLiabilitiesRecordedatFairValueonaRecurringBasisDetails" xlink:type="simple" xlink:href="fnlc-20260331.xsd#FairValueAssetsandLiabilitiesRecordedatFairValueonaRecurringBasisDetails"/>
  <link:definitionLink xlink:role="http://www.thefirst.com/role/FairValueAssetsandLiabilitiesRecordedatFairValueonaRecurringBasisDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_463374f8-b47c-416d-8a69-822aa30e7e3d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_a5ee6316-d62d-4834-badb-0b4642dfb981" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_463374f8-b47c-416d-8a69-822aa30e7e3d" xlink:to="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_a5ee6316-d62d-4834-badb-0b4642dfb981" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByMeasurementFrequencyAxis_93179944-bab2-4320-8dc3-3d649ef0f69e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueByMeasurementFrequencyAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_a5ee6316-d62d-4834-badb-0b4642dfb981" xlink:to="loc_us-gaap_FairValueByMeasurementFrequencyAxis_93179944-bab2-4320-8dc3-3d649ef0f69e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementFrequencyDomain_93179944-bab2-4320-8dc3-3d649ef0f69e_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueMeasurementFrequencyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByMeasurementFrequencyAxis_93179944-bab2-4320-8dc3-3d649ef0f69e" xlink:to="loc_us-gaap_FairValueMeasurementFrequencyDomain_93179944-bab2-4320-8dc3-3d649ef0f69e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementFrequencyDomain_0e89debc-b766-4fcc-b80e-9d2990f5ab36" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueMeasurementFrequencyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByMeasurementFrequencyAxis_93179944-bab2-4320-8dc3-3d649ef0f69e" xlink:to="loc_us-gaap_FairValueMeasurementFrequencyDomain_0e89debc-b766-4fcc-b80e-9d2990f5ab36" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsRecurringMember_2d8a6432-261e-4dcc-9875-8fcacbaf777c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueMeasurementsRecurringMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementFrequencyDomain_0e89debc-b766-4fcc-b80e-9d2990f5ab36" xlink:to="loc_us-gaap_FairValueMeasurementsRecurringMember_2d8a6432-261e-4dcc-9875-8fcacbaf777c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByMeasurementBasisAxis_8ea3f3a7-4203-4c0d-867a-d212430ee2f1" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueByMeasurementBasisAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_a5ee6316-d62d-4834-badb-0b4642dfb981" xlink:to="loc_us-gaap_FairValueByMeasurementBasisAxis_8ea3f3a7-4203-4c0d-867a-d212430ee2f1" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_8ea3f3a7-4203-4c0d-867a-d212430ee2f1_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PortionAtFairValueFairValueDisclosureMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByMeasurementBasisAxis_8ea3f3a7-4203-4c0d-867a-d212430ee2f1" xlink:to="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_8ea3f3a7-4203-4c0d-867a-d212430ee2f1_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueDisclosureItemAmountsDomain_b6d758eb-9e0b-4f04-a5a8-69de0e3548b3" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueDisclosureItemAmountsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByMeasurementBasisAxis_8ea3f3a7-4203-4c0d-867a-d212430ee2f1" xlink:to="loc_us-gaap_FairValueDisclosureItemAmountsDomain_b6d758eb-9e0b-4f04-a5a8-69de0e3548b3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_aa5d3737-4dc6-4e3a-9b7d-b78bcee9e08a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PortionAtFairValueFairValueDisclosureMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueDisclosureItemAmountsDomain_b6d758eb-9e0b-4f04-a5a8-69de0e3548b3" xlink:to="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_aa5d3737-4dc6-4e3a-9b7d-b78bcee9e08a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EstimateOfFairValueFairValueDisclosureMember_690f27a9-3122-43e4-83cc-a9e74b34079c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EstimateOfFairValueFairValueDisclosureMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_aa5d3737-4dc6-4e3a-9b7d-b78bcee9e08a" xlink:to="loc_us-gaap_EstimateOfFairValueFairValueDisclosureMember_690f27a9-3122-43e4-83cc-a9e74b34079c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_a0172db3-0dcf-42e4-aadc-acfd6a208ea3" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_a5ee6316-d62d-4834-badb-0b4642dfb981" xlink:to="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_a0172db3-0dcf-42e4-aadc-acfd6a208ea3" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_a0172db3-0dcf-42e4-aadc-acfd6a208ea3_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_a0172db3-0dcf-42e4-aadc-acfd6a208ea3" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_a0172db3-0dcf-42e4-aadc-acfd6a208ea3_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_6fae7af4-b317-4d59-adb6-e1f109590f75" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_a0172db3-0dcf-42e4-aadc-acfd6a208ea3" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_6fae7af4-b317-4d59-adb6-e1f109590f75" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel1Member_0c00c80e-a7a0-4399-81cf-953989eb1f45" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueInputsLevel1Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_6fae7af4-b317-4d59-adb6-e1f109590f75" xlink:to="loc_us-gaap_FairValueInputsLevel1Member_0c00c80e-a7a0-4399-81cf-953989eb1f45" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel2Member_2d63b80a-652a-4341-b962-90cbb53e471a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueInputsLevel2Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_6fae7af4-b317-4d59-adb6-e1f109590f75" xlink:to="loc_us-gaap_FairValueInputsLevel2Member_2d63b80a-652a-4341-b962-90cbb53e471a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel3Member_ed4e7406-75b0-4c42-b091-39c8f9f9b46f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueInputsLevel3Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_6fae7af4-b317-4d59-adb6-e1f109590f75" xlink:to="loc_us-gaap_FairValueInputsLevel3Member_ed4e7406-75b0-4c42-b091-39c8f9f9b46f" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancialInstrumentAxis_f5f4b0b8-f066-486d-9f46-03c13c13b3e5" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FinancialInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_a5ee6316-d62d-4834-badb-0b4642dfb981" xlink:to="loc_us-gaap_FinancialInstrumentAxis_f5f4b0b8-f066-486d-9f46-03c13c13b3e5" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_f5f4b0b8-f066-486d-9f46-03c13c13b3e5_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FinancialInstrumentAxis_f5f4b0b8-f066-486d-9f46-03c13c13b3e5" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_f5f4b0b8-f066-486d-9f46-03c13c13b3e5_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_2a75331b-f3e1-4cf2-8a9b-a7b63ce059e2" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FinancialInstrumentAxis_f5f4b0b8-f066-486d-9f46-03c13c13b3e5" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_2a75331b-f3e1-4cf2-8a9b-a7b63ce059e2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_USTreasuryAndGovernmentMember_3cad8198-15ff-420e-8d01-0dd9a62a3c54" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_USTreasuryAndGovernmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_2a75331b-f3e1-4cf2-8a9b-a7b63ce059e2" xlink:to="loc_us-gaap_USTreasuryAndGovernmentMember_3cad8198-15ff-420e-8d01-0dd9a62a3c54" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MortgageBackedSecuritiesMember_9115c5c9-ac36-47be-ae6f-c7ce1a8fa68d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_MortgageBackedSecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_2a75331b-f3e1-4cf2-8a9b-a7b63ce059e2" xlink:to="loc_us-gaap_MortgageBackedSecuritiesMember_9115c5c9-ac36-47be-ae6f-c7ce1a8fa68d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_USStatesAndPoliticalSubdivisionsMember_0ff2d0d4-b1f5-452f-bc63-68583f268909" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_USStatesAndPoliticalSubdivisionsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_2a75331b-f3e1-4cf2-8a9b-a7b63ce059e2" xlink:to="loc_us-gaap_USStatesAndPoliticalSubdivisionsMember_0ff2d0d4-b1f5-452f-bc63-68583f268909" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetBackedSecuritiesMember_5fed614c-27d0-4780-9576-0bfb353e82ee" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AssetBackedSecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_2a75331b-f3e1-4cf2-8a9b-a7b63ce059e2" xlink:to="loc_us-gaap_AssetBackedSecuritiesMember_5fed614c-27d0-4780-9576-0bfb353e82ee" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentRiskAxis_3e67d30f-b380-4ca0-bd33-3f02d1b6e23a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeInstrumentRiskAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_a5ee6316-d62d-4834-badb-0b4642dfb981" xlink:to="loc_us-gaap_DerivativeInstrumentRiskAxis_3e67d30f-b380-4ca0-bd33-3f02d1b6e23a" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_3e67d30f-b380-4ca0-bd33-3f02d1b6e23a_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_3e67d30f-b380-4ca0-bd33-3f02d1b6e23a" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_3e67d30f-b380-4ca0-bd33-3f02d1b6e23a_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_d9fc4622-03cc-468e-bd68-093e944117af" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_3e67d30f-b380-4ca0-bd33-3f02d1b6e23a" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_d9fc4622-03cc-468e-bd68-093e944117af" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestRateCapMember_4e31844f-5b8e-4b6a-95ba-3aa1fb434d18" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_InterestRateCapMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_d9fc4622-03cc-468e-bd68-093e944117af" xlink:to="loc_us-gaap_InterestRateCapMember_4e31844f-5b8e-4b6a-95ba-3aa1fb434d18" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestRateSwapMember_70f01934-9300-45e0-b9f1-70c7dc71c40b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_InterestRateSwapMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_d9fc4622-03cc-468e-bd68-093e944117af" xlink:to="loc_us-gaap_InterestRateSwapMember_70f01934-9300-45e0-b9f1-70c7dc71c40b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_fnlc_CustomerLoanInterestSwapMember_8232ebd1-df0a-4913-83d1-786da3539564" xlink:href="fnlc-20260331.xsd#fnlc_CustomerLoanInterestSwapMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_d9fc4622-03cc-468e-bd68-093e944117af" xlink:to="loc_fnlc_CustomerLoanInterestSwapMember_8232ebd1-df0a-4913-83d1-786da3539564" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesAvailableForSaleExcludingAccruedInterest_040b1b29-47cc-436a-8adc-ade06ccb6db5" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtSecuritiesAvailableForSaleExcludingAccruedInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_463374f8-b47c-416d-8a69-822aa30e7e3d" xlink:to="loc_us-gaap_DebtSecuritiesAvailableForSaleExcludingAccruedInterest_040b1b29-47cc-436a-8adc-ade06ccb6db5" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeAssets_f29b5fad-8a4c-4706-9259-efcfd167d276" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_463374f8-b47c-416d-8a69-822aa30e7e3d" xlink:to="loc_us-gaap_DerivativeAssets_f29b5fad-8a4c-4706-9259-efcfd167d276" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsFairValueDisclosure_54d01074-26ec-4ecb-963a-c1b2c8aa98dd" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AssetsFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_463374f8-b47c-416d-8a69-822aa30e7e3d" xlink:to="loc_us-gaap_AssetsFairValueDisclosure_54d01074-26ec-4ecb-963a-c1b2c8aa98dd" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeLiabilities_4f32e6bd-8bb0-43d4-ae62-c0d616e3aa36" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeLiabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_463374f8-b47c-416d-8a69-822aa30e7e3d" xlink:to="loc_us-gaap_DerivativeLiabilities_4f32e6bd-8bb0-43d4-ae62-c0d616e3aa36" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.thefirst.com/role/FairValueAssetsRecordedatFairValueonaNonRecurringBasisDetails" xlink:type="simple" xlink:href="fnlc-20260331.xsd#FairValueAssetsRecordedatFairValueonaNonRecurringBasisDetails"/>
  <link:definitionLink xlink:role="http://www.thefirst.com/role/FairValueAssetsRecordedatFairValueonaNonRecurringBasisDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_a8a137e5-f25e-456b-be6e-5310ade4af7e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_0c9fbd1d-0a43-4d6b-9a3e-a6633b97273f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_a8a137e5-f25e-456b-be6e-5310ade4af7e" xlink:to="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_0c9fbd1d-0a43-4d6b-9a3e-a6633b97273f" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByMeasurementFrequencyAxis_58827fa5-705b-486b-a689-121be5ff7478" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueByMeasurementFrequencyAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_0c9fbd1d-0a43-4d6b-9a3e-a6633b97273f" xlink:to="loc_us-gaap_FairValueByMeasurementFrequencyAxis_58827fa5-705b-486b-a689-121be5ff7478" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementFrequencyDomain_58827fa5-705b-486b-a689-121be5ff7478_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueMeasurementFrequencyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByMeasurementFrequencyAxis_58827fa5-705b-486b-a689-121be5ff7478" xlink:to="loc_us-gaap_FairValueMeasurementFrequencyDomain_58827fa5-705b-486b-a689-121be5ff7478_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementFrequencyDomain_c4937b3d-10bc-4586-96cb-7ed5ef97c1bc" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueMeasurementFrequencyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByMeasurementFrequencyAxis_58827fa5-705b-486b-a689-121be5ff7478" xlink:to="loc_us-gaap_FairValueMeasurementFrequencyDomain_c4937b3d-10bc-4586-96cb-7ed5ef97c1bc" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsNonrecurringMember_16f1d2f4-cdad-478d-a723-951c18e00214" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueMeasurementsNonrecurringMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementFrequencyDomain_c4937b3d-10bc-4586-96cb-7ed5ef97c1bc" xlink:to="loc_us-gaap_FairValueMeasurementsNonrecurringMember_16f1d2f4-cdad-478d-a723-951c18e00214" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByMeasurementBasisAxis_9d53479a-54a2-4f40-b0ea-443c62445b7c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueByMeasurementBasisAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_0c9fbd1d-0a43-4d6b-9a3e-a6633b97273f" xlink:to="loc_us-gaap_FairValueByMeasurementBasisAxis_9d53479a-54a2-4f40-b0ea-443c62445b7c" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_9d53479a-54a2-4f40-b0ea-443c62445b7c_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PortionAtFairValueFairValueDisclosureMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByMeasurementBasisAxis_9d53479a-54a2-4f40-b0ea-443c62445b7c" xlink:to="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_9d53479a-54a2-4f40-b0ea-443c62445b7c_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueDisclosureItemAmountsDomain_fe63f16c-6100-4ea5-96f2-6969563ae8e6" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueDisclosureItemAmountsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByMeasurementBasisAxis_9d53479a-54a2-4f40-b0ea-443c62445b7c" xlink:to="loc_us-gaap_FairValueDisclosureItemAmountsDomain_fe63f16c-6100-4ea5-96f2-6969563ae8e6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_2d7e242e-6593-4e29-8aec-73843515af5d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PortionAtFairValueFairValueDisclosureMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueDisclosureItemAmountsDomain_fe63f16c-6100-4ea5-96f2-6969563ae8e6" xlink:to="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_2d7e242e-6593-4e29-8aec-73843515af5d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EstimateOfFairValueFairValueDisclosureMember_3ae31dcb-71d2-4ff0-b882-4d6250663dfa" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EstimateOfFairValueFairValueDisclosureMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_2d7e242e-6593-4e29-8aec-73843515af5d" xlink:to="loc_us-gaap_EstimateOfFairValueFairValueDisclosureMember_3ae31dcb-71d2-4ff0-b882-4d6250663dfa" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_0242582f-6409-4b51-ab9a-4af942b9ccb9" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_0c9fbd1d-0a43-4d6b-9a3e-a6633b97273f" xlink:to="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_0242582f-6409-4b51-ab9a-4af942b9ccb9" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_0242582f-6409-4b51-ab9a-4af942b9ccb9_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_0242582f-6409-4b51-ab9a-4af942b9ccb9" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_0242582f-6409-4b51-ab9a-4af942b9ccb9_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_ade2d42e-cf14-4a9c-95b7-700ffc47f976" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_0242582f-6409-4b51-ab9a-4af942b9ccb9" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_ade2d42e-cf14-4a9c-95b7-700ffc47f976" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel1Member_c8d2ae80-70b0-4fd6-af30-ca32124b5952" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueInputsLevel1Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_ade2d42e-cf14-4a9c-95b7-700ffc47f976" xlink:to="loc_us-gaap_FairValueInputsLevel1Member_c8d2ae80-70b0-4fd6-af30-ca32124b5952" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel2Member_193653ee-66a1-4bea-8863-97c01cbbb592" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueInputsLevel2Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_ade2d42e-cf14-4a9c-95b7-700ffc47f976" xlink:to="loc_us-gaap_FairValueInputsLevel2Member_193653ee-66a1-4bea-8863-97c01cbbb592" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel3Member_107d6360-2b07-4114-bb74-1d0a37654822" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueInputsLevel3Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_ade2d42e-cf14-4a9c-95b7-700ffc47f976" xlink:to="loc_us-gaap_FairValueInputsLevel3Member_107d6360-2b07-4114-bb74-1d0a37654822" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ServicingAssetAtFairValueAmount_a92ba2f5-0929-4cda-965b-f14bf8ed14a6" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ServicingAssetAtFairValueAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_a8a137e5-f25e-456b-be6e-5310ade4af7e" xlink:to="loc_us-gaap_ServicingAssetAtFairValueAmount_a92ba2f5-0929-4cda-965b-f14bf8ed14a6" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_fnlc_ImpairedLoansFairValueDisclosure_08cb27d2-9800-4b8f-b4ad-f2ff69261039" xlink:href="fnlc-20260331.xsd#fnlc_ImpairedLoansFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_a8a137e5-f25e-456b-be6e-5310ade4af7e" xlink:to="loc_fnlc_ImpairedLoansFairValueDisclosure_08cb27d2-9800-4b8f-b4ad-f2ff69261039" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsFairValueDisclosure_bec0de6e-e9af-4641-a40d-da3b60866679" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AssetsFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_a8a137e5-f25e-456b-be6e-5310ade4af7e" xlink:to="loc_us-gaap_AssetsFairValueDisclosure_bec0de6e-e9af-4641-a40d-da3b60866679" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.thefirst.com/role/FairValueCarryingAmountsandEstimatedFairValuesDetails" xlink:type="simple" xlink:href="fnlc-20260331.xsd#FairValueCarryingAmountsandEstimatedFairValuesDetails"/>
  <link:definitionLink xlink:role="http://www.thefirst.com/role/FairValueCarryingAmountsandEstimatedFairValuesDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueBalanceSheetGroupingFinancialStatementCaptionsLineItems_b45076af-4152-4671-8684-8410860dbfc8" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueBalanceSheetGroupingFinancialStatementCaptionsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByBalanceSheetGroupingTable_c68ccbb6-d9bb-419c-bf50-cce5f8d33ef8" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueByBalanceSheetGroupingTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FairValueBalanceSheetGroupingFinancialStatementCaptionsLineItems_b45076af-4152-4671-8684-8410860dbfc8" xlink:to="loc_us-gaap_FairValueByBalanceSheetGroupingTable_c68ccbb6-d9bb-419c-bf50-cce5f8d33ef8" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByMeasurementBasisAxis_2b688de2-bdf1-4b70-a5f9-77b67a7ad460" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueByMeasurementBasisAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueByBalanceSheetGroupingTable_c68ccbb6-d9bb-419c-bf50-cce5f8d33ef8" xlink:to="loc_us-gaap_FairValueByMeasurementBasisAxis_2b688de2-bdf1-4b70-a5f9-77b67a7ad460" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_2b688de2-bdf1-4b70-a5f9-77b67a7ad460_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PortionAtFairValueFairValueDisclosureMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByMeasurementBasisAxis_2b688de2-bdf1-4b70-a5f9-77b67a7ad460" xlink:to="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_2b688de2-bdf1-4b70-a5f9-77b67a7ad460_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueDisclosureItemAmountsDomain_33cd156d-ae8e-4283-bdde-1e74dca27e60" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueDisclosureItemAmountsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByMeasurementBasisAxis_2b688de2-bdf1-4b70-a5f9-77b67a7ad460" xlink:to="loc_us-gaap_FairValueDisclosureItemAmountsDomain_33cd156d-ae8e-4283-bdde-1e74dca27e60" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_0548a401-6c66-43c1-8fed-f05fd832b290" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PortionAtFairValueFairValueDisclosureMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueDisclosureItemAmountsDomain_33cd156d-ae8e-4283-bdde-1e74dca27e60" xlink:to="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_0548a401-6c66-43c1-8fed-f05fd832b290" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CarryingReportedAmountFairValueDisclosureMember_042c5e22-1443-4bf5-af07-9171df6bb6e2" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CarryingReportedAmountFairValueDisclosureMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_0548a401-6c66-43c1-8fed-f05fd832b290" xlink:to="loc_us-gaap_CarryingReportedAmountFairValueDisclosureMember_042c5e22-1443-4bf5-af07-9171df6bb6e2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EstimateOfFairValueFairValueDisclosureMember_98aa1433-0107-4de6-abab-484a4ab575fd" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EstimateOfFairValueFairValueDisclosureMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_0548a401-6c66-43c1-8fed-f05fd832b290" xlink:to="loc_us-gaap_EstimateOfFairValueFairValueDisclosureMember_98aa1433-0107-4de6-abab-484a4ab575fd" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_73362ade-22ca-4af6-8723-fc105fcfd7d9" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueByBalanceSheetGroupingTable_c68ccbb6-d9bb-419c-bf50-cce5f8d33ef8" xlink:to="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_73362ade-22ca-4af6-8723-fc105fcfd7d9" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_73362ade-22ca-4af6-8723-fc105fcfd7d9_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_73362ade-22ca-4af6-8723-fc105fcfd7d9" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_73362ade-22ca-4af6-8723-fc105fcfd7d9_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_2d19db2b-3bb3-4f01-a393-51b1381faa4a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_73362ade-22ca-4af6-8723-fc105fcfd7d9" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_2d19db2b-3bb3-4f01-a393-51b1381faa4a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel1Member_ef3db758-ba23-4464-bfb9-6b2846d0712b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueInputsLevel1Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_2d19db2b-3bb3-4f01-a393-51b1381faa4a" xlink:to="loc_us-gaap_FairValueInputsLevel1Member_ef3db758-ba23-4464-bfb9-6b2846d0712b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel2Member_5b35b2ff-c88e-4522-8095-1512a90762d2" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueInputsLevel2Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_2d19db2b-3bb3-4f01-a393-51b1381faa4a" xlink:to="loc_us-gaap_FairValueInputsLevel2Member_5b35b2ff-c88e-4522-8095-1512a90762d2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel3Member_e75c6a85-28a5-4eda-86ab-5f8ac15b5ea2" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueInputsLevel3Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_2d19db2b-3bb3-4f01-a393-51b1381faa4a" xlink:to="loc_us-gaap_FairValueInputsLevel3Member_e75c6a85-28a5-4eda-86ab-5f8ac15b5ea2" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivablePortfolioSegmentAxis_b71b0cde-cca5-40cd-aecc-443a9b3c0d88" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FinancingReceivablePortfolioSegmentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueByBalanceSheetGroupingTable_c68ccbb6-d9bb-419c-bf50-cce5f8d33ef8" xlink:to="loc_us-gaap_FinancingReceivablePortfolioSegmentAxis_b71b0cde-cca5-40cd-aecc-443a9b3c0d88" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_b71b0cde-cca5-40cd-aecc-443a9b3c0d88_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FinancingReceivablePortfolioSegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FinancingReceivablePortfolioSegmentAxis_b71b0cde-cca5-40cd-aecc-443a9b3c0d88" xlink:to="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_b71b0cde-cca5-40cd-aecc-443a9b3c0d88_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_838d57c2-6133-43f1-9e7d-e4ba46a7ee0e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FinancingReceivablePortfolioSegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FinancingReceivablePortfolioSegmentAxis_b71b0cde-cca5-40cd-aecc-443a9b3c0d88" xlink:to="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_838d57c2-6133-43f1-9e7d-e4ba46a7ee0e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommercialPortfolioSegmentMember_9575350d-0b5e-4e72-b0fe-ee055af3d8df" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CommercialPortfolioSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_838d57c2-6133-43f1-9e7d-e4ba46a7ee0e" xlink:to="loc_us-gaap_CommercialPortfolioSegmentMember_9575350d-0b5e-4e72-b0fe-ee055af3d8df" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_fnlc_MunicipalPortfolioSegmentMember_1013abf4-2463-4530-a222-8038cdcfd215" xlink:href="fnlc-20260331.xsd#fnlc_MunicipalPortfolioSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_838d57c2-6133-43f1-9e7d-e4ba46a7ee0e" xlink:to="loc_fnlc_MunicipalPortfolioSegmentMember_1013abf4-2463-4530-a222-8038cdcfd215" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ResidentialPortfolioSegmentMember_4727a59e-d0e7-4c54-a33f-56a20b653848" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ResidentialPortfolioSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_838d57c2-6133-43f1-9e7d-e4ba46a7ee0e" xlink:to="loc_us-gaap_ResidentialPortfolioSegmentMember_4727a59e-d0e7-4c54-a33f-56a20b653848" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_fnlc_HomeEquityLineOfCreditPortfolioMember_a26a24f7-826f-4d5b-9ba9-429c721c36ef" xlink:href="fnlc-20260331.xsd#fnlc_HomeEquityLineOfCreditPortfolioMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_838d57c2-6133-43f1-9e7d-e4ba46a7ee0e" xlink:to="loc_fnlc_HomeEquityLineOfCreditPortfolioMember_a26a24f7-826f-4d5b-9ba9-429c721c36ef" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConsumerPortfolioSegmentMember_9c0c1b0f-09d3-4f3f-b061-376d7bf6b7c4" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ConsumerPortfolioSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivablePortfolioSegmentDomain_838d57c2-6133-43f1-9e7d-e4ba46a7ee0e" xlink:to="loc_us-gaap_ConsumerPortfolioSegmentMember_9c0c1b0f-09d3-4f3f-b061-376d7bf6b7c4" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis_c8d58995-1613-4fd2-966f-4911f30412af" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueByBalanceSheetGroupingTable_c68ccbb6-d9bb-419c-bf50-cce5f8d33ef8" xlink:to="loc_us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis_c8d58995-1613-4fd2-966f-4911f30412af" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_c8d58995-1613-4fd2-966f-4911f30412af_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis_c8d58995-1613-4fd2-966f-4911f30412af" xlink:to="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_c8d58995-1613-4fd2-966f-4911f30412af_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_22e72449-d227-4f01-ab5c-66fbcc090787" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis_c8d58995-1613-4fd2-966f-4911f30412af" xlink:to="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_22e72449-d227-4f01-ab5c-66fbcc090787" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RealEstateLoanMember_e03c4d52-be39-4a2d-8a67-b559cad1a06d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RealEstateLoanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_22e72449-d227-4f01-ab5c-66fbcc090787" xlink:to="loc_us-gaap_RealEstateLoanMember_e03c4d52-be39-4a2d-8a67-b559cad1a06d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConstructionLoansMember_184b3bab-e49a-46dd-8f37-79283365012e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ConstructionLoansMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_22e72449-d227-4f01-ab5c-66fbcc090787" xlink:to="loc_us-gaap_ConstructionLoansMember_184b3bab-e49a-46dd-8f37-79283365012e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_fnlc_OtherLoansMember_4a62f291-e759-47ac-a6b5-2dcc5145dc7e" xlink:href="fnlc-20260331.xsd#fnlc_OtherLoansMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_22e72449-d227-4f01-ab5c-66fbcc090787" xlink:to="loc_fnlc_OtherLoansMember_4a62f291-e759-47ac-a6b5-2dcc5145dc7e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_fnlc_TermLoanMember_998db84e-a0c6-46ef-aab5-24300ffafce3" xlink:href="fnlc-20260331.xsd#fnlc_TermLoanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_22e72449-d227-4f01-ab5c-66fbcc090787" xlink:to="loc_fnlc_TermLoanMember_998db84e-a0c6-46ef-aab5-24300ffafce3" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancialInstrumentsFinancialAssetsBalanceSheetGroupingsAbstract_40c39442-71fe-403c-b786-5fa292baf173" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FinancialInstrumentsFinancialAssetsBalanceSheetGroupingsAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueBalanceSheetGroupingFinancialStatementCaptionsLineItems_b45076af-4152-4671-8684-8410860dbfc8" xlink:to="loc_us-gaap_FinancialInstrumentsFinancialAssetsBalanceSheetGroupingsAbstract_40c39442-71fe-403c-b786-5fa292baf173" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HeldToMaturitySecuritiesFairValue_279c39fd-c103-46c9-bd64-affec6d3ba7f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_HeldToMaturitySecuritiesFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancialInstrumentsFinancialAssetsBalanceSheetGroupingsAbstract_40c39442-71fe-403c-b786-5fa292baf173" xlink:to="loc_us-gaap_HeldToMaturitySecuritiesFairValue_279c39fd-c103-46c9-bd64-affec6d3ba7f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LoansReceivableFairValueDisclosure_eaf226d1-5ae9-4a04-9142-34f009e86dac" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LoansReceivableFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancialInstrumentsFinancialAssetsBalanceSheetGroupingsAbstract_40c39442-71fe-403c-b786-5fa292baf173" xlink:to="loc_us-gaap_LoansReceivableFairValueDisclosure_eaf226d1-5ae9-4a04-9142-34f009e86dac" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ServicingAssetAtFairValueAmount_5f0a7069-0415-432d-b7bf-ea513f053843" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ServicingAssetAtFairValueAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancialInstrumentsFinancialAssetsBalanceSheetGroupingsAbstract_40c39442-71fe-403c-b786-5fa292baf173" xlink:to="loc_us-gaap_ServicingAssetAtFairValueAmount_5f0a7069-0415-432d-b7bf-ea513f053843" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancialInstrumentsFinancialLiabilitiesBalanceSheetGroupingsAbstract_03ff146d-120f-4f03-a83b-60bbbc251c87" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FinancialInstrumentsFinancialLiabilitiesBalanceSheetGroupingsAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueBalanceSheetGroupingFinancialStatementCaptionsLineItems_b45076af-4152-4671-8684-8410860dbfc8" xlink:to="loc_us-gaap_FinancialInstrumentsFinancialLiabilitiesBalanceSheetGroupingsAbstract_03ff146d-120f-4f03-a83b-60bbbc251c87" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TimeDeposits_1f7196f0-54ad-4dc6-988b-4cec363940a4" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TimeDeposits"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancialInstrumentsFinancialLiabilitiesBalanceSheetGroupingsAbstract_03ff146d-120f-4f03-a83b-60bbbc251c87" xlink:to="loc_us-gaap_TimeDeposits_1f7196f0-54ad-4dc6-988b-4cec363940a4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_fnlc_NationalCertificatesOfDeposit_061c8827-d767-4cb2-8615-1517548f6916" xlink:href="fnlc-20260331.xsd#fnlc_NationalCertificatesOfDeposit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancialInstrumentsFinancialLiabilitiesBalanceSheetGroupingsAbstract_03ff146d-120f-4f03-a83b-60bbbc251c87" xlink:to="loc_fnlc_NationalCertificatesOfDeposit_061c8827-d767-4cb2-8615-1517548f6916" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Deposits_b51c8fc1-8daf-46ab-a6cd-32f173358d35" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_Deposits"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancialInstrumentsFinancialLiabilitiesBalanceSheetGroupingsAbstract_03ff146d-120f-4f03-a83b-60bbbc251c87" xlink:to="loc_us-gaap_Deposits_b51c8fc1-8daf-46ab-a6cd-32f173358d35" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsSoldUnderAgreementsToRepurchaseRepurchaseLiability_ce97205c-7cf5-4768-b873-6192ba104c6c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AssetsSoldUnderAgreementsToRepurchaseRepurchaseLiability"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancialInstrumentsFinancialLiabilitiesBalanceSheetGroupingsAbstract_03ff146d-120f-4f03-a83b-60bbbc251c87" xlink:to="loc_us-gaap_AssetsSoldUnderAgreementsToRepurchaseRepurchaseLiability_ce97205c-7cf5-4768-b873-6192ba104c6c" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FederalHomeLoanBankAdvancesLongTerm_e345ba41-8bc8-4e1c-ae50-dda99c0dab96" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FederalHomeLoanBankAdvancesLongTerm"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancialInstrumentsFinancialLiabilitiesBalanceSheetGroupingsAbstract_03ff146d-120f-4f03-a83b-60bbbc251c87" xlink:to="loc_us-gaap_FederalHomeLoanBankAdvancesLongTerm_e345ba41-8bc8-4e1c-ae50-dda99c0dab96" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtAndCapitalLeaseObligations_0eaf097a-f224-429a-ad34-759f703b4140" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtAndCapitalLeaseObligations"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancialInstrumentsFinancialLiabilitiesBalanceSheetGroupingsAbstract_03ff146d-120f-4f03-a83b-60bbbc251c87" xlink:to="loc_us-gaap_DebtAndCapitalLeaseObligations_0eaf097a-f224-429a-ad34-759f703b4140" xlink:type="arc" order="6"/>
  </link:definitionLink>
</link:linkbase>
