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          <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AccountingPoliciesAbstract" xlink:label="us-gaap_AccountingPoliciesAbstract"/>
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          <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ClassOfStockDomain" xlink:label="us-gaap_ClassOfStockDomain"/>
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          <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1" xlink:label="us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1"/>
          <link:loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_EntityEmergingGrowthCompany" xlink:label="dei_EntityEmergingGrowthCompany"/>
          <link:loc xlink:type="locator" xlink:href="fisi-20260630.xsd#fisi_ChiefCommercialBankingOfficerMember" xlink:label="fisi_ChiefCommercialBankingOfficerMember"/>
          <link:loc xlink:type="locator" xlink:href="fisi-20260630.xsd#fisi_ChiefHumanResourceOfficerMember" xlink:label="fisi_ChiefHumanResourceOfficerMember"/>
          <link:loc xlink:type="locator" xlink:href="fisi-20260630.xsd#fisi_ChiefLegalOfficerMember" xlink:label="fisi_ChiefLegalOfficerMember"/>
          <link:loc xlink:type="locator" xlink:href="fisi-20260630.xsd#fisi_ChiefMarketingOfficerMember" xlink:label="fisi_ChiefMarketingOfficerMember"/>
          <link:loc xlink:type="locator" xlink:href="fisi-20260630.xsd#fisi_ChiefConsumerBankingOfficerMember" xlink:label="fisi_ChiefConsumerBankingOfficerMember"/>
          <link:loc xlink:type="locator" xlink:href="fisi-20260630.xsd#fisi_ChiefRiskOfficerMember" xlink:label="fisi_ChiefRiskOfficerMember"/>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ScheduleOfCashFlowSupplementalDisclosuresTableTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Summary of Supplemental Cash Flow Information</link:label>
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          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FinancingReceivablesEqualToGreaterThan90DaysPastDueMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Greater than 90 Days [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FinancingReceivablesEqualToGreaterThan90DaysPastDueMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Financial Asset, Equal to or Greater than 90 Days Past Due [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FinancingReceivablesEqualToGreaterThan90DaysPastDueMember_lbl" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">90+ Days Past Due</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FinancingReceivableAllowanceForCreditLossesWriteOffs_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Financing Receivable, Allowance for Credit Loss, Writeoff, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FinancingReceivableAllowanceForCreditLossesWriteOffs_lbl" xlink:role="http://www.xbrl.org/2009/role/negatedLabel">Charge-offs</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FinancingReceivableAllowanceForCreditLossesWriteOffs_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Financing Receivable, Allowance for Credit Loss, Writeoff</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueInRollingYearThree_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Lessee, Operating Lease, Liability, to be Paid, Rolling Year Three</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueInRollingYearThree_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">2028</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FinancingReceivableOriginatedTwoYearsBeforeLatestFiscalYear_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Prior Fiscal Year 2</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FinancingReceivableOriginatedTwoYearsBeforeLatestFiscalYear_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Financing Receivable, Year Three, Originated, Two Years before Current Fiscal Year</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_EntityIncorporationStateCountryCode_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Entity Incorporation, State or Country Code</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_EntityIncorporationStateCountryCode_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Entity Incorporation, State or Country Code</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PreferredStockSharesIssued_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Preferred stock, shares issued</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PreferredStockSharesIssued_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Preferred Stock, Shares Issued</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PreferredStockSharesIssued_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Preferred Stock, Shares Issued, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_BalanceSheetLocationDomain_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Balance Sheet Location</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_BalanceSheetLocationDomain_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Statement of Financial Position Location, Balance [Domain]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_OperatingLeaseRightOfUseAssetAccumulatedAmortization_lbl" xlink:role="http://www.xbrl.org/2009/role/negatedLabel">Accumulated amortization</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_OperatingLeaseRightOfUseAssetAccumulatedAmortization_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Operating Lease Right Of Use Asset Accumulated Amortization</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_OperatingLeaseRightOfUseAssetAccumulatedAmortization_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Operating lease right of use asset accumulated amortization.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_CreditRiskContractMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Credit Contract [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_CreditRiskContractMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Credit Risk Contract [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_CashFlowNoncashInvestingAndFinancingActivitiesDisclosureAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Cash Flow, Noncash Investing and Financing Activities Disclosure [Abstract]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_CashFlowNoncashInvestingAndFinancingActivitiesDisclosureAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Noncash investing and financing activities:</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AvailableForSaleSecuritiesDebtMaturitiesWithinOneYearFairValue_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Debt securities available for sale, Due in one year or less, Fair Value</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AvailableForSaleSecuritiesDebtMaturitiesWithinOneYearFairValue_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Debt Securities, Available-for-Sale, Fair Value, Maturity, Allocated and Single Maturity Date, Year One</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FinancingReceivablePortfolioSegmentAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Financing Receivable Portfolio Segment [Axis]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLonger_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Securities available for sale, 12 months or longer, Fair Value</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLonger_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Debt Securities, Available-for-Sale, Continuous Unrealized Loss Position, 12 Months or Longer</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLonger_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Debt Securities Available For Sale Continuous Unrealized Loss Position12 Months Or Longer, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_EntityCurrentReportingStatus_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Entity Current Reporting Status</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_EntityCurrentReportingStatus_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Entity Current Reporting Status</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_OtherRealEstateOwnedOtherReceivableMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Other Real Estate Owned [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_OtherRealEstateOwnedOtherReceivableMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Other Real Estate Owned Other Receivable [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_OtherRealEstateOwnedOtherReceivableMember_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Other real estate owned other receivable.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OtherComprehensiveIncomeLossBeforeReclassificationsBeforeTax_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Other Comprehensive Income (Loss), before Reclassifications, before Tax</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OtherComprehensiveIncomeLossBeforeReclassificationsBeforeTax_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Other comprehensive income (loss), before Reclassifications, Pre-tax Amount</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Class of Financing Receivable</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Class of Financing Receivable [Axis]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_MunicipalBondsMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Municipal Bonds [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_MunicipalBondsMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Municipal Bonds [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FairValueInputsLevel2Member_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Level 2 Inputs [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FairValueInputsLevel2Member_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Fair Value, Inputs, Level 2 [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_CommitmentsAndContingenciesDisclosureTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Commitments and Contingencies</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_CommitmentsAndContingenciesDisclosureTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Commitments and Contingencies Disclosure [Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_CashFlowHedgingMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Cash Flow Hedge of Interest Rate Risk [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_CashFlowHedgingMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Cash Flow Hedging [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_CashFlowHedgingMember_lbl" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Cash Flow Hedging [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_CommonStockSharesAuthorized_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Common stock, shares authorized</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_CommonStockSharesAuthorized_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Common Stock, Shares Authorized</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearFour_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Finite-Lived Intangible Asset, Expected Amortization, Year Four</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearFour_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">2030</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Fair Value by Liability Class</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Fair Value by Liability Class [Domain]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_DocumentFiscalPeriodFocus_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Document Fiscal Period Focus</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_DocumentFiscalPeriodFocus_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Document Fiscal Period Focus</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OperatingLeaseRightOfUseAssetStatementOfFinancialPositionExtensibleList_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Operating Lease, Right-of-Use Asset, Statement of Financial Position [Extensible List]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OperatingLeaseRightOfUseAssetStatementOfFinancialPositionExtensibleList_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Operating Lease, Right-of-Use Asset, Statement of Financial Position [Extensible Enumeration]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_EntityShellCompany_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Entity Shell Company</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_EntityShellCompany_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Entity Shell Company</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueInRollingYearFour_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Lessee, Operating Lease, Liability, to be Paid, Rolling Year Four</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueInRollingYearFour_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">2029</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DividendsCommonStockCash_lbl" xlink:role="http://www.xbrl.org/2009/role/negatedLabel">Common stock dividends per share</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DividendsCommonStockCash_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Dividends, Common Stock, Cash</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_CashAndCashEquivalentsAtCarryingValue_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Cash and Cash Equivalent</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_CashAndCashEquivalentsAtCarryingValue_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Total cash and cash equivalents</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_CashAndCashEquivalentsAtCarryingValue_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Total cash and cash equivalents</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_USGovernmentSponsoredEnterprisesDebtSecuritiesMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">U.S. Government Agency And Government Sponsored Enterprises [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_USGovernmentSponsoredEnterprisesDebtSecuritiesMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">US Government-sponsored Enterprises Debt Securities [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_CommonStockSharesIssued_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Common stock, shares issued</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_CommonStockSharesIssued_lbl" xlink:role="http://www.xbrl.org/2003/role/periodStartLabel">Shares issued, beginning balance</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_CommonStockSharesIssued_lbl" xlink:role="http://www.xbrl.org/2003/role/periodEndLabel">Shares issued, ending balance</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_CommonStockSharesIssued_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Common Stock, Shares, Issued</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_CommonStockSharesIssued_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Common Stock, Shares, Issued, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_MortgageBackedSecuritiesAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Mortgage Backed Securities [Axis]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_MortgageBackedSecuritiesAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Mortgage Backed Securities</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_LesseeOperatingLeaseDescription_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Operating leases term description</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_LesseeOperatingLeaseDescription_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Lessee, Operating Lease, Description</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AllowanceForNotesAndLoansReceivableCurrent_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Financing Receivable, Allowance for Credit Loss, Current</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AllowanceForNotesAndLoansReceivableCurrent_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Financing Receivable, Allowance for Credit Loss, Current</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Asset Class</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Asset Class [Domain]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_NoninterestIncomeLoanServicing_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Loan servicing</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_NoninterestIncomeLoanServicing_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Noninterest Income Loan Servicing</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_NoninterestIncomeLoanServicing_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Noninterest income loan servicing.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_StatementTable_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Statement [Table]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_StatementTable_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Statement [Table]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_RightOfUseAssetObtainedInExchangeForOperatingLeaseLiability_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Right of use assets obtained in exchange for new operating lease liabilities</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_RightOfUseAssetObtainedInExchangeForOperatingLeaseLiability_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Right-of-Use Asset Obtained in Exchange for Operating Lease Liability</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_InterestReceivable_lbl" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Accrued interest receivable</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_InterestReceivable_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Accrued interest receivable</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_InterestReceivable_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Interest Receivable</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_NoninterestBearingDepositLiabilities_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Noninterest-bearing demand</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_NoninterestBearingDepositLiabilities_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Noninterest-Bearing Deposit Liabilities</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_NoninterestBearingDepositLiabilities_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Noninterest-bearing Deposit Liabilities, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_LesseeOperatingSubleaseResidualValueGuaranteeDescription_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Lessee, Operating Sublease, Residual Value Guarantee, Description</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_LesseeOperatingSubleaseResidualValueGuaranteeDescription_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Description of residual value guarantee</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FinancingReceivableOriginatedFourYearsBeforeLatestFiscalYear_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Prior Fiscal Year 4</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FinancingReceivableOriginatedFourYearsBeforeLatestFiscalYear_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Financing Receivable, Year Five, Originated, Four Years before Current Fiscal Year</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_HeldToMaturitySecuritiesDebtMaturitiesAfterOneThroughFiveYearsNetCarryingAmount_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Debt Securities, Held-to-Maturity, Amortized Cost, after Allowance for Credit Loss, Maturity, Allocated and Single Maturity Date, after Year One through Five</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_HeldToMaturitySecuritiesDebtMaturitiesAfterOneThroughFiveYearsNetCarryingAmount_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Debt securities held to maturity, Due after one to five years, Amortized Cost</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_StockRepurchaseProgramRemainingNumberOfSharesAuthorizedToBeRepurchased_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Share Repurchase Program, Remaining Authorized, Number of Shares</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_StockRepurchaseProgramRemainingNumberOfSharesAuthorizedToBeRepurchased_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Shares remain available for repurchase</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_OtherAssetsAndOtherLiabilitiesDisclosureTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">The entire disclosure for other assets and other liabilities.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_OtherAssetsAndOtherLiabilitiesDisclosureTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Other Assets and Other Liabilities Disclosure [Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_OtherAssetsAndOtherLiabilitiesDisclosureTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Other Assets and Other Liabilities</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_StatementLineItems_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Statement [Line Items]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_StatementLineItems_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Statement [Line Items]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_TreasuryStockValueAcquiredCostMethod_lbl" xlink:role="http://www.xbrl.org/2009/role/negatedLabel">Purchases of common stock for treasury</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_TreasuryStockValueAcquiredCostMethod_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Treasury Stock, Value, Acquired, Cost Method</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_EntityFilerCategory_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Entity Filer Category</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_EntityFilerCategory_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Entity Filer Category</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PriorPeriodReclassificationAdjustmentDescription_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Reclassifications</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PriorPeriodReclassificationAdjustmentDescription_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Reclassification, Comparability Adjustment [Policy Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FinancingReceivables60To89DaysPastDueMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">60 to 89 Days Past Due [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FinancingReceivables60To89DaysPastDueMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Financial Asset, 60 to 89 Days Past Due [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ScheduleOfFinancingReceivablesPastDueTable_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Schedule Of Financing Receivables Past Due [Table]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ScheduleOfFinancingReceivablesPastDueTable_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Financing Receivable, Past Due [Table]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DerivativeGainLossStatementOfIncomeOrComprehensiveIncomeExtensibleEnumeration_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Derivative, Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DerivativeGainLossStatementOfIncomeOrComprehensiveIncomeExtensibleEnumeration_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Derivative, Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_ScheduleOfLeaseCostsAndOtherLeaseInformationTableTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Summary of Lease Costs and Other Lease Information</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_ScheduleOfLeaseCostsAndOtherLeaseInformationTableTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Schedule Of Lease Costs And Other Lease Information Table [Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_ScheduleOfLeaseCostsAndOtherLeaseInformationTableTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Schedule of lease costs and other lease information.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_LiabilitiesAndStockholdersEquity_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Total liabilities and shareholders&#8217; equity</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_LiabilitiesAndStockholdersEquity_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Liabilities and Equity</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DebtInstrumentLineItems_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Debt Instrument [Line Items]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FinancingReceivableAllowanceForCreditLossesRecovery_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Recoveries</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FinancingReceivableAllowanceForCreditLossesRecovery_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Financing Receivable, Allowance for Credit Loss, Recovery</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_NoninterestIncome_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Noninterest Income</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_NoninterestIncome_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Total noninterest income</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_NoninterestIncome_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Noninterest income</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_NoninterestIncome_lbl" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Noninterest (loss) income</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_NoninterestIncome_lbl" xlink:role="http://www.xbrl.org/2009/role/netLabel">Noninterest income</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_ResidentialCollateralizedMortgageMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Residential Collateralized Mortgage [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_ResidentialCollateralizedMortgageMember_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Residential collateralized mortgage.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AcceleratedShareRepurchasesFinalPricePaidPerShare_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Share repurchase program at an average price</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AcceleratedShareRepurchasesFinalPricePaidPerShare_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Accelerated Share Repurchases, Final Price Paid Per Share</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FairValueByBalanceSheetGroupingTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Carrying Amount, Estimated Fair Value, and Placement in Fair Value Hierarchy of Financial Instruments</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FairValueByBalanceSheetGroupingTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Fair Value, by Balance Sheet Grouping [Table Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Hedging Relationship</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Hedging Relationship [Axis]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AccumulatedDefinedBenefitPlansAdjustmentNetGainLossIncludingPortionAttributableToNoncontrollingInterestMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Accumulated Defined Benefit Plans Adjustment, Net Gain (Loss) Including Portion Attributable to Noncontrolling Interest [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AccumulatedDefinedBenefitPlansAdjustmentNetGainLossIncludingPortionAttributableToNoncontrollingInterestMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Accumulated Defined Benefit Plans Adjustment, Net Gain (Loss) Including Portion Attributable to Noncontrolling Interest [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_CollateralDependentLoansOnBusinessAssets_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Collateral dependent loans on business assets</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_CollateralDependentLoansOnBusinessAssets_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Collateral Dependent Loans On Business Assets</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_CollateralDependentLoansOnBusinessAssets_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Collateral dependent loans on business assets.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_CashAndCashEquivalentsFairValueDisclosure_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Cash and cash equivalents</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_CashAndCashEquivalentsFairValueDisclosure_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Cash and Cash Equivalents, Fair Value Disclosure</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FiniteLivedIntangibleAssetsRemainingAmortizationPeriod1_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Weighted average remaining amortization period for other intangibles</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FiniteLivedIntangibleAssetsRemainingAmortizationPeriod1_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Finite-Lived Intangible Assets, Remaining Amortization Period</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FinancingReceivables30To59DaysPastDueMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">30 to 59 Days Past Due [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FinancingReceivables30To59DaysPastDueMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Financial Asset, 30 to 59 Days Past Due [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DefinedBenefitPlanNetPeriodicBenefitCostCreditExcludingServiceCostStatementOfIncomeOrComprehensiveIncomeExtensibleList_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Defined Benefit Plan, Net Periodic Benefit Cost (Credit) Excluding Service Cost, Statement of Income or Comprehensive Income [Extensible Enumeration]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_Goodwill_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Goodwill</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_Goodwill_lbl" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Carrying amount of goodwill</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_Goodwill_lbl" xlink:role="http://www.xbrl.org/2003/role/periodStartLabel">Goodwill, beginning balance</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_Goodwill_lbl" xlink:role="http://www.xbrl.org/2003/role/periodEndLabel">Goodwill, ending balance</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_Goodwill_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Goodwill</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_Goodwill_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Goodwill, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_TransferToOtherRealEstate_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Real Estate Owned, Transfer to Real Estate Owned</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_TransferToOtherRealEstate_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Real estate and other assets acquired in settlement of loans</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_IncomeLossBeforeProvisionForCreditLossesAndIncomeTaxes_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Income (Loss) Before Provision For Credit Losses And Income Taxes</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_IncomeLossBeforeProvisionForCreditLossesAndIncomeTaxes_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Income (loss) before provision for credit losses and income taxes.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_IncomeLossBeforeProvisionForCreditLossesAndIncomeTaxes_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Income before provision for credit losses and income taxes</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterTenYearsAmortizedCost_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Debt securities available for sale, Due after ten years, Amortized Cost</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterTenYearsAmortizedCost_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Debt Securities, Available-for-Sale, Amortized Cost, Maturity, Allocated and Single Maturity Date, after Year 10</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ReconciliationOfOperatingProfitLossFromSegmentsToConsolidatedTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Reconciliation of Operating Profit (Loss) from Segments to Consolidated [Table Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ReconciliationOfOperatingProfitLossFromSegmentsToConsolidatedTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Segment Profit (Loss)</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_InterestRateSwapTransactionTwoMember_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Interest rate swap transaction two.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_InterestRateSwapTransactionTwoMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Interest Rate Swap Transaction Two [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_InterestRateSwapTransactionTwoMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Interest Rate Swap Transaction Two [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_HeldToMaturitySecuritiesDebtMaturitiesAfterTenYearsNetCarryingAmount_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Debt securities held to maturity, Due after ten years, Amortized Cost</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_HeldToMaturitySecuritiesDebtMaturitiesAfterTenYearsNetCarryingAmount_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Debt Securities, Held-to-Maturity, Amortized Cost, after Allowance for Credit Loss, Maturity, Allocated and Single Maturity Date, after Year 10</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_ConsumerOverdraftsMember_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Consumer Overdrafts [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_ConsumerOverdraftsMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Consumer Overdrafts [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_ConsumerOverdraftsMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Consumer Overdrafts [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_NonperformingFinancingReceivableMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Non-Performing [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_NonperformingFinancingReceivableMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Nonperforming Financial Instruments [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_UnrealizedLossOnInvestmentsTableTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Investments Gross Unrealized Losses and Fair Value</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_UnrealizedLossOnInvestmentsTableTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Unrealized Loss on Investments [Table Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_UnrealizedLossOnInvestmentsTableTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Tabular disclosure of unrealized loss on investments.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DepositsFairValueDisclosure_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Time deposits</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DepositsFairValueDisclosure_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Deposits, Fair Value Disclosure</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ScheduleOfEarningsPerShareBasicAndDilutedTableTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Reconciliation of Earnings and Shares Used in Calculating Basic and Diluted EPS</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ScheduleOfEarningsPerShareBasicAndDilutedTableTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Schedule of Earnings Per Share, Basic and Diluted [Table Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_SpecialMentionMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Special Mention [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_SpecialMentionMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Special Mention [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PaymentsToAcquireLifeInsurancePolicies_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Payment to Acquire Life Insurance Policy, Investing Activities</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PaymentsToAcquireLifeInsurancePolicies_lbl" xlink:role="http://www.xbrl.org/2009/role/negatedLabel">Purchase of company owned life insurance</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Investment, Name [Axis]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DividendsPayableCurrentAndNoncurrent_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Dividends Payable</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DividendsPayableCurrentAndNoncurrent_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Accrued and declared unpaid dividends</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_InvestmentsClassifiedByContractualMaturityDateTableTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Scheduled Maturities of Securities Available for Sale and Securities Held to Maturity</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_InvestmentsClassifiedByContractualMaturityDateTableTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Investments Classified by Contractual Maturity Date [Table Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_EarningsPerShareBasic_lbl" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Basic earnings per common share</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_EarningsPerShareBasic_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Basic</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_EarningsPerShareBasic_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Earnings Per Share, Basic</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_EarningsPerShareBasic_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Earnings Per Share, Basic, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_RepaymentsOfLongTermDebt_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Repayments of Long-Term Debt</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_RepaymentsOfLongTermDebt_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Repayments of Long-Term Debt, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_RepaymentsOfLongTermDebt_lbl" xlink:role="http://www.xbrl.org/2009/role/negatedLabel">Repayment of long-term borrowings</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_HeldToMaturitySecuritiesAccumulatedUnrecognizedHoldingGain_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Securities held to maturity, Unrealized Gains</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_HeldToMaturitySecuritiesAccumulatedUnrecognizedHoldingGain_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Debt Securities, Held-to-Maturity, Accumulated Unrecognized Gain</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PensionAndOtherPostretirementBenefitsDisclosureTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Employee Benefit Plans</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PensionAndOtherPostretirementBenefitsDisclosureTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Retirement Benefits [Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ShareBasedCompensationAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Share-based compensation plans:</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ShareBasedCompensationAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Share-Based Payment Arrangement, Noncash Expense [Abstract]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_ResidentialRealEstateMortgagesServicedForOthers_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Residential real estate mortgages serviced for others</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_ResidentialRealEstateMortgagesServicedForOthers_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Residential Real Estate Mortgages Serviced For Others</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_ResidentialRealEstateMortgagesServicedForOthers_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Residential Real Estate Mortgages Serviced For Others</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PaymentsForProceedsFromLoansAndLeases_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Payments for (Proceeds from) Loans and Leases</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PaymentsForProceedsFromLoansAndLeases_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Payments for (Proceeds from) Loans and Leases, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PaymentsForProceedsFromLoansAndLeases_lbl" xlink:role="http://www.xbrl.org/2009/role/negatedLabel">Net increase in loans</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_CollateralDependentLoansOnRealProperty_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Collateral dependent loans on real property</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_CollateralDependentLoansOnRealProperty_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Collateral Dependent Loans On Real Property</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_CollateralDependentLoansOnRealProperty_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Collateral dependent loans on real property.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Adjustments to reconcile net income to net cash provided by operating activities:</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Adjustment to Reconcile Net Income to Cash Provided by (Used in) Operating Activity [Abstract]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_HedgingDesignationDomain_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Hedging Designation</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_HedgingDesignationDomain_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Hedging Designation [Domain]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FinancingReceivableAllowanceForCreditLossesLineItems_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Financing Receivable, Allowance for Credit Losses [Line Items]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FinancingReceivableAllowanceForCreditLossesLineItems_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Financing Receivable, Allowance for Credit Loss [Line Items]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_EquityMethodInvestmentQuotedMarketValue_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Equity Method Investment, Quoted Market Value</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_EquityMethodInvestmentQuotedMarketValue_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Net proceeds from sale of securities to purchase investment</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_LoansHeldForSaleMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Loans Held For Sale [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_LoansHeldForSaleMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Loans Held For Sale [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_LoansHeldForSaleMember_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Loans held for sale.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AdjustmentsForNewAccountingPronouncementsAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Accounting Standards Update</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AdjustmentsForNewAccountingPronouncementsAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Accounting Standards Update [Axis]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="srt_ConsolidationItemsDomain_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Consolidation Items</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="srt_ConsolidationItemsDomain_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Consolidation Items [Domain]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_MortgageBankingMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Mortgage Banking [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_MortgageBankingMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Mortgage Banking [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_CreditLossBenefitExpense_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Credit Loss Benefit Expense</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_CreditLossBenefitExpense_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Credit loss benefit expense.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_CreditLossBenefitExpense_lbl" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Credit loss (benefit) for unfunded commitments</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_StockholdersEquityAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Shareholders&#8217; equity:</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_StockholdersEquityAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Equity, Attributable to Parent [Abstract]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FinancingReceivableNonaccrualInterestIncome_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Interest income on nonaccrual loans</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FinancingReceivableNonaccrualInterestIncome_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Financing Receivable, Nonaccrual, Interest Income</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_EntitySmallBusiness_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Entity Small Business</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_EntitySmallBusiness_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Entity Small Business</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_InterestAndDividendIncomeOperatingAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Interest income:</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_InterestAndDividendIncomeOperatingAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Interest and Dividend Income, Operating [Abstract]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_HedgingDesignationAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Hedging Designation</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_HedgingDesignationAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Hedging Designation [Axis]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_CollateralizedMortgageBackedSecuritiesFederalHomeLoanMortgageCorporationCertificatesAndObligationsFhlmcMember_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Collateralized Mortgage-Backed Securities Federal Home Loan Mortgage Corporation Certificates and Obligations (FHLMC).</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_CollateralizedMortgageBackedSecuritiesFederalHomeLoanMortgageCorporationCertificatesAndObligationsFhlmcMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Collateralized Mortgage-Backed Securities Federal Home Loan Mortgage Corporation Certificates and Obligations (FHLMC) [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_RetainedEarningsAccumulatedDeficit_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Retained earnings</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_RetainedEarningsAccumulatedDeficit_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Retained Earnings (Accumulated Deficit)</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_RetainedEarningsAccumulatedDeficit_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Retained Earnings (Accumulated Deficit), Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_RetainedEarningsAccumulatedDeficit_lbl" xlink:role="http://www.xbrl.org/2003/role/periodStartLabel">Retained Earnings (Accumulated Deficit), Beginning Balance</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_RetainedEarningsAccumulatedDeficit_lbl" xlink:role="http://www.xbrl.org/2003/role/periodEndLabel">Retained Earnings (Accumulated Deficit), Ending Balance</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DebtSecuritiesHeldToMaturityAllowanceForCreditLoss_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Securities held to maturity, allowance for credit losses</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DebtSecuritiesHeldToMaturityAllowanceForCreditLoss_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Debt Securities, Held-to-Maturity, Allowance for Credit Loss</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DebtSecuritiesHeldToMaturityAllowanceForCreditLoss_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Debt Securities, Held-to-maturity, Allowance for Credit Loss, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DebtSecuritiesHeldToMaturityAllowanceForCreditLoss_lbl" xlink:role="http://www.xbrl.org/2003/role/periodStartLabel">Debt Securities, Held-to-maturity, Allowance for Credit Loss, Beginning Balance</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DebtSecuritiesHeldToMaturityAllowanceForCreditLoss_lbl" xlink:role="http://www.xbrl.org/2003/role/periodEndLabel">Debt Securities, Held-to-maturity, Allowance for Credit Loss, Ending Balance</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PreferredStockMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Preferred Equity [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PreferredStockMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Preferred Stock [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_CollateralizedMortgageObligationsFederalNationalMortgageAssociationCertificatesAndObligationsFnmaMember_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Collateralized Mortgage Obligations Federal National Mortgage Association Certificates and Obligations (FNMA).</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_CollateralizedMortgageObligationsFederalNationalMortgageAssociationCertificatesAndObligationsFnmaMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Collateralized Mortgage Obligations Federal National Mortgage Association Certificates and Obligations (FNMA) [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DisclosureOfCompensationRelatedCostsShareBasedPaymentsTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Share-Based Compensation Plans</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DisclosureOfCompensationRelatedCostsShareBasedPaymentsTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Share-Based Payment Arrangement [Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueInRollingYearTwo_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Lessee, Operating Lease, Liability, to be Paid, Rolling Year Two</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueInRollingYearTwo_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">2027</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DefinedContributionPlanTable_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Defined Contribution Plan [Table]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DefinedContributionPlanTable_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Defined Contribution Plan [Table]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PaymentsOfDividends_lbl" xlink:role="http://www.xbrl.org/2009/role/negatedLabel">Cash dividends paid to common and preferred shareholders</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PaymentsOfDividends_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Payments of Dividends</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PaymentsOfDividends_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Payments of Dividends, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_LeasesAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Leases [Abstract]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AccumulatedDefinedBenefitPlansAdjustmentIncludingPortionAttributableToNoncontrollingInterestMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Accumulated Defined Benefit Plans Adjustment Including Portion Attributable to Noncontrolling Interest [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AccumulatedDefinedBenefitPlansAdjustmentIncludingPortionAttributableToNoncontrollingInterestMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Accumulated Defined Benefit Plans Adjustment Including Portion Attributable to Noncontrolling Interest [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_UnderwrittenPublicOfferingMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Underwritten Public Offering [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_UnderwrittenPublicOfferingMember_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Underwritten public offering member</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_UnderwrittenPublicOfferingMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Underwritten public offering [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_AmendmentFlag_lbl" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Amendment Flag</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_AmendmentFlag_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Amendment Flag</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_InterestIncomeSecuritiesTaxable_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Interest Income, Securities, Operating, Taxable</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_InterestIncomeSecuritiesTaxable_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Taxable interest and dividends</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_LiabilitiesAndStockholdersEquityAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">LIABILITIES AND SHAREHOLDERS&#8217; EQUITY</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_LiabilitiesAndStockholdersEquityAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Liabilities and Equity [Abstract]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_EntityAddressPostalZipCode_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Entity Address, Postal Zip Code</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_EntityAddressPostalZipCode_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Entity Address, Postal Zip Code</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_NetCashProvidedByUsedInOperatingActivities_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Cash Provided by (Used in) Operating Activity, Including Discontinued Operation</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_NetCashProvidedByUsedInOperatingActivities_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Net cash provided by operating activities</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_SubstandardMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Substandard [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_SubstandardMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Substandard [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_SegmentReportingCodmProfitLossMeasureHowUsedDescription_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Segment Reporting, CODM, Profit (Loss) Measure, How Used, Description</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_CommonStockMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Common Stock [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_CommonStockMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Common Stock [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_CommonStockMember_lbl" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Common shares [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FinancingReceivableNonaccrualNoAllowance_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Nonaccrual with no allowance</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FinancingReceivableNonaccrualNoAllowance_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Financing Receivable, Nonaccrual, No Allowance</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_SalariesAndEmployeeBenefitsMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Salaries and Employee Benefits [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_SalariesAndEmployeeBenefitsMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Salaries And Employee Benefits [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_SalariesAndEmployeeBenefitsMember_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Salaries and Employee Benefits [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DefinedContributionPlanEmployerDiscretionaryContributionAmount_lbl" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Employer contribution</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DefinedContributionPlanEmployerDiscretionaryContributionAmount_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Defined Contribution Plan, Employer Discretionary Contribution Amount</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_HedgingRelationshipDomain_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Hedging Relationship</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_HedgingRelationshipDomain_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Hedging Relationship [Domain]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ScheduleOfDerivativeInstrumentsInStatementOfFinancialPositionFairValueTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Fair Values of Derivative Instruments on the Balance Sheet</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ScheduleOfDerivativeInstrumentsInStatementOfFinancialPositionFairValueTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Schedule of Derivative Instruments in Statement of Financial Position, Fair Value [Table Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_NatureOfBusinessOperationsPolicyTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Nature of Operations</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_NatureOfBusinessOperationsPolicyTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Nature Of Business Operations Policy [Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_NatureOfBusinessOperationsPolicyTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Nature Of Business Operations [Policy Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PortionAtFairValueFairValueDisclosureMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Fair Value Disclosure Item Amounts [Default]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PortionAtFairValueFairValueDisclosureMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Portion at Fair Value Measurement [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PortionAtFairValueFairValueDisclosureMember_lbl" xlink:role="http://fasb.org/us-gaap/role/label/axisDefault">Portion at Fair Value Measurement [Member] [Default]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_EntityAddressAddressLine1_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Entity Address, Address Line One</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_EntityAddressAddressLine1_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Entity Address, Address Line One</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_InvestmentSecuritiesAccumulatedUnrecognizedHoldingLoss_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Investment Securities Accumulated Unrecognized Holding Loss</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_InvestmentSecuritiesAccumulatedUnrecognizedHoldingLoss_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Amount of accumulated pre-tax unrealized loss on securities.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_InvestmentSecuritiesAccumulatedUnrecognizedHoldingLoss_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Total AFS debt securities with unrealized losses, Unrealized Losses</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FairValueByFairValueHierarchyLevelAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Fair Value Hierarchy and NAV</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FairValueByFairValueHierarchyLevelAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Fair Value Hierarchy and NAV [Axis]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ShorttermDebtFairValue_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Short-term borrowings</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ShorttermDebtFairValue_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Short-Term Debt, Fair Value</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_EarningsPerShareAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Earnings Per Share [Abstract]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_EarningsPerShareAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Earnings per common share (Note 2):</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ConsumerPortfolioSegmentMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Other Consumer [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ConsumerPortfolioSegmentMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Consumer Portfolio Segment [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_SupplementalCashFlowInformationAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Supplemental Cash Flow Information [Abstract]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_SupplementalCashFlowInformationAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Supplemental information:</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_SupplementalCashFlowInformationAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Supplemental information:</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_CollateralDependentFinancingReceivableMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Collateral Dependent Loans [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_CollateralDependentFinancingReceivableMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Collateral Dependent Financing Receivable [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_CollateralDependentFinancingReceivableMember_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Collateral dependent financing receivable.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DerivativeAssets_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Derivative Asset</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DerivativeAssets_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Derivative instruments, assets</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DerivativeAssets_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Derivative Asset, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_GoodwillAndIntangibleAssetsDisclosureTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Goodwill and Other Intangible Assets</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_GoodwillAndIntangibleAssetsDisclosureTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Goodwill and Intangible Assets Disclosure [Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OtherLiabilitiesMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Other Liabilities [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OtherLiabilitiesMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Other Liabilities [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_ShareholdersEquityLineItems_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Shareholders Equity [Line Items]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_ShareholdersEquityLineItems_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Shareholders Equity [Line Items]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_ShareholdersEquityLineItems_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Shareholders Equity [Line Items]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_BalanceSheetLocationAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Balance Sheet Location</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_BalanceSheetLocationAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Statement of Financial Position Location, Balance [Axis]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_InvestmentTypeAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Investment Type [Axis]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_InvestmentTypeAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Investment Type</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_InterestIncomeSecuritiesTaxExempt_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Interest Income, Securities, Operating, Tax Exempt</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_InterestIncomeSecuritiesTaxExempt_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Tax-exempt interest and dividends</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OperatingLeaseRightOfUseAsset_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Net book value</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OperatingLeaseRightOfUseAsset_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Operating lease right of use assets</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OperatingLeaseRightOfUseAsset_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Operating Lease, Right-of-Use Asset</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DebtSecuritiesAvailableForSaleUnrealizedLossPosition_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Securities available for sale, Fair Value, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DebtSecuritiesAvailableForSaleUnrealizedLossPosition_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Debt Securities, Available-for-Sale, Unrealized Loss Position</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodBeforeTax_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Reclassification, Pre-tax Amount</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodBeforeTax_lbl" xlink:role="http://www.xbrl.org/2009/role/negatedLabel">Reclassification, Pre-tax Amount</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodBeforeTax_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Reclassification from Accumulated Other Comprehensive Income, Current Period, before Tax</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodBeforeTax_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Total reclassified for the period</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodBeforeTax_lbl" xlink:role="http://www.xbrl.org/2009/role/negatedTerseLabel">Reclassification before tax</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PaymentsToAcquireAvailableForSaleSecuritiesDebt_lbl" xlink:role="http://www.xbrl.org/2009/role/negatedLabel">Purchases of available for sale securities</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PaymentsToAcquireAvailableForSaleSecuritiesDebt_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Payments to Acquire Debt Securities, Available-for-Sale</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OtherComprehensiveIncomeLossAvailableForSaleSecuritiesAdjustmentNetOfTax_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Securities available for sale and transferred securities</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OtherComprehensiveIncomeLossAvailableForSaleSecuritiesAdjustmentNetOfTax_lbl" xlink:role="http://www.xbrl.org/2003/role/label">OCI, Debt Securities, Available-for-Sale, Gain (Loss), after Adjustment and Tax</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OtherComprehensiveIncomeLossAvailableForSaleSecuritiesAdjustmentNetOfTax_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">OCI, Debt Securities, Available-for-Sale, Gain (Loss), after Adjustment and Tax, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_MeasurementInputComparabilityAdjustmentMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Appraisal Adjustments [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_MeasurementInputComparabilityAdjustmentMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Measurement Input, Comparability Adjustment [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_DocumentType_lbl" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Document Type</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_DocumentType_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Document Type</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_IncomeTaxesPaidNet_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Income Taxes Paid, Net</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_IncomeTaxesPaidNet_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Income Taxes Paid, Net, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_IncomeTaxesPaidNet_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Cash paid for income taxes</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FinancingReceivableModificationsPostModificationRecordedInvestment2_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Financing Receivable, Modified in Period, Amount</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FinancingReceivableModificationsPostModificationRecordedInvestment2_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Amortized cost basis</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_CommitmentsToExtendCreditMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Commitments To Extend Credit [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_CommitmentsToExtendCreditMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Commitments to Extend Credit [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_EntityCentralIndexKey_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Entity Central Index Key</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_EntityCentralIndexKey_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Entity Central Index Key</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DerivativeAssetFairValueOfCollateral_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Derivative Asset, Fair Value of Collateral</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DerivativeAssetFairValueOfCollateral_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Collateral on derivative instruments</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_InterestBearingDepositsInBanks_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Interest-Bearing Deposits in Banks and Other Financial Institutions</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_InterestBearingDepositsInBanks_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Interest-bearing deposits in other banks</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ValuationTechniqueAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Valuation Approach and Technique</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ValuationTechniqueAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Valuation Approach and Technique [Axis]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseIncludingExchangeRateEffect_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Cash, Cash Equivalent, Restricted Cash, and Restricted Cash Equivalent, Period Increase (Decrease), Including Exchange Rate Effect and Discontinued Operation</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseIncludingExchangeRateEffect_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Net (decrease) increase in cash and cash equivalents</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AccruedInvestmentIncomeReceivable_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Accrued interest receivable</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AccruedInvestmentIncomeReceivable_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Accrued Investment Income Receivable</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AccruedInvestmentIncomeReceivable_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Accrued Investment Income Receivable, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Antidilutive shares excluded from computation of diluted EPS</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_HeldToMaturitySecuritiesDebtMaturitiesAfterFiveThroughTenYearsNetCarryingAmount_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Debt securities held to maturity, Due after five years through ten years, Amortized Cost</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_HeldToMaturitySecuritiesDebtMaturitiesAfterFiveThroughTenYearsNetCarryingAmount_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Debt Securities, Held-to-Maturity, Amortized Cost, after Allowance for Credit Loss, Maturity, Allocated and Single Maturity Date, after Year 5 through 10</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_CommonStockParOrStatedValuePerShare_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Common stock, par value</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_CommonStockParOrStatedValuePerShare_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Common Stock, Par or Stated Value Per Share</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_CommonStockParOrStatedValuePerShare_lbl" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Share Price</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_TypeOfAdoptionMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Accounting Standards Update</link:label>
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          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_GoodwillLineItems_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Goodwill [Line Items]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_GoodwillLineItems_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Goodwill [Line Items]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FinancingReceivableRecordedInvestmentLineItems_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Financing Receivable Recorded Investment [Line Items]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FinancingReceivableRecordedInvestmentLineItems_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Financing Receivable, Credit Quality Indicator [Line Items]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_SeriesB1EightPointFourEightPercentagePreferredStockMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Series B-1 8.48% Preferred Stock [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_SeriesB1EightPointFourEightPercentagePreferredStockMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Series B1 Eight Point Four Eight Percentage Preferred Stock [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_SeriesB1EightPointFourEightPercentagePreferredStockMember_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Series B-1 Eight Point four eight percentage preferred stock.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_IncreaseDecreaseInOtherOperatingLiabilities_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Increase (Decrease) in Other Operating Liabilities</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_IncreaseDecreaseInOtherOperatingLiabilities_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Increase (Decrease) in Other Operating Liabilities, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_IncreaseDecreaseInOtherOperatingLiabilities_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Decrease in other liabilities</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis_lbl" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Securities available for sale, Amortized Cost</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Securities available for sale, Amortized Cost</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Debt Securities, Available-for-Sale, Amortized Cost</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Securities available for sale, at fair value, amortized cost</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DefinedContributionPlanDisclosureLineItems_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Defined Contribution Plan Disclosure [Line Items]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DefinedContributionPlanDisclosureLineItems_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Defined Contribution Plan Disclosure [Line Items]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AvailableForSaleSecuritiesDebtSecurities_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Securities available for sale</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AvailableForSaleSecuritiesDebtSecurities_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Debt securities available for sale, Fair Value</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AvailableForSaleSecuritiesDebtSecurities_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Debt Securities, Available-for-Sale</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AvailableForSaleSecuritiesDebtSecurities_lbl" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Securities available for sale, at fair value (amortized cost of $959,631 and $958,142, respectively)</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_NoninterestIncomeAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Noninterest income:</link:label>
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          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_CashFlowReportingPolicyTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Cash Flow Reporting</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_CashFlowReportingPolicyTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Cash Flow Reporting Policy [Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_CashFlowReportingPolicyTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Cash flow reporting.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DoubtfulMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Doubtful [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DoubtfulMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Doubtful [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossAfterReclassificationAndTax_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Hedging derivative instruments</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossAfterReclassificationAndTax_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), after Reclassification and Tax</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossAfterReclassificationAndTax_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), after Reclassification and Tax, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DerivativeTable_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Derivative [Table]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ProceedsFromSaleOfLoansHeldForSale_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Proceeds from sale of loans held for sale</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ProceedsFromSaleOfLoansHeldForSale_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Proceeds from Sale, Loan, Held-for-Sale</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ProceedsFromSaleOfLoansHeldForSale_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Proceeds from Sale of Loans Held-for-sale, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Reclassification out of Accumulated Other Comprehensive Income</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Reclassification out of Accumulated Other Comprehensive Income [Axis]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_EstimateOfFairValueFairValueDisclosureMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Estimated Fair Value [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_EstimateOfFairValueFairValueDisclosureMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Estimate of Fair Value Measurement [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DerivativeNotionalAmount_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Gross notional amount</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DerivativeNotionalAmount_lbl" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Notional amount</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DerivativeNotionalAmount_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Derivative, Notional Amount</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_CurrentFiscalYearEndDate_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Current Fiscal Year End Date</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_CurrentFiscalYearEndDate_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Current Fiscal Year End Date</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DebtInstrumentTable_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Schedule of Long-Term Debt Instruments [Table]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_DocumentQuarterlyReport_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Document Quarterly Report</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_DocumentQuarterlyReport_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Document Quarterly Report</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FairValueByBalanceSheetGroupingTable_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Fair Value By Balance Sheet Grouping [Table]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FairValueByBalanceSheetGroupingTable_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Fair Value, by Balance Sheet Grouping [Table]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_RealizedGainLossOnInvestmentsTableTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Realized Gain (Loss) on Investments [Table Text Block]</link:label>
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          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_EntityAddressStateOrProvince_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Entity Address, State or Province</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_EntityAddressStateOrProvince_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Entity Address, State or Province</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_InvestmentSecuritiesInUnrealizedLossPositionsTwelveMonthsOrLongerQualitativeDisclosureNumberOfPositions_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Number of security positions, unrealized loss position for more than 12 months</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_InvestmentSecuritiesInUnrealizedLossPositionsTwelveMonthsOrLongerQualitativeDisclosureNumberOfPositions_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Investment Securities In Unrealized Loss Positions Twelve Months Or Longer Qualitative Disclosure Number Of Positions</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_InvestmentSecuritiesInUnrealizedLossPositionsTwelveMonthsOrLongerQualitativeDisclosureNumberOfPositions_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Disclosure regarding factors used to determine that the impairment of securities not categorized as either held-to-maturity securities or trading securities (hence equal to available for sale securities) where cost exceeds fair value is not an other than temporary impairment (OTTI). This item contains disclosure of the number of investment positions in the available-for-sale investments determined to be temporarily impaired for twelve months or longer.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ProceedsFromRepaymentsOfShortTermDebt_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Proceeds from (Repayments of) Short-Term Debt</link:label>
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          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_InformationTechnologyAndDataProcessing_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Computer and data processing</link:label>
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          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="srt_EquityMethodInvesteeNameDomain_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Investment, Name [Domain]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ComprehensiveIncomeNetOfTax_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Comprehensive Income (Loss), Net of Tax, Attributable to Parent</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ComprehensiveIncomeNetOfTax_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Comprehensive income</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Securities available for sale, Unrealized Gains</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Debt Securities, Available-for-Sale, Accumulated Gross Unrealized Gain, before Tax</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax_lbl" xlink:role="http://www.xbrl.org/2009/role/negatedLabel">Securities available for sale, Unrealized Gains</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_DebtSecuritiesAvailableForSaleAndHeldToMaturityRestricted_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Debt securities available for sale and held to maturity restricted.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_DebtSecuritiesAvailableForSaleAndHeldToMaturityRestricted_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Securities pledged as collateral</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_DebtSecuritiesAvailableForSaleAndHeldToMaturityRestricted_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Debt Securities Available For Sale And Held To Maturity Restricted</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_IncrementalCommonSharesAttributableToShareBasedPaymentArrangements_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Exercise of stock options</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_IncrementalCommonSharesAttributableToShareBasedPaymentArrangements_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Incremental Common Shares Attributable to Dilutive Effect of Share-Based Payment Arrangements</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_IncrementalCommonSharesAttributableToShareBasedPaymentArrangements_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Incremental Common Shares Attributable to Share-based Payment Arrangements, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_NonOwnerOccupiedMortgageMember_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Non-owner occupied mortgage.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_NonOwnerOccupiedMortgageMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Non-Owner Occupied Mortgage [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_NonOwnerOccupiedMortgageMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Non-Owner Occupied [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_InternalCreditAssessmentAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Internal Credit Assessment</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_InternalCreditAssessmentAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Internal Credit Assessment [Axis]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Share-Based Payment Arrangement, Expensed and Capitalized, Amount [Table Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Share-Based Compensation Expense and The Total Income Tax Benefit Included In Consolidated Statements of Operations</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ProfessionalFees_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Professional services</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ProfessionalFees_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Professional Fees</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_InterestAndOtherIncome_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Other interest income</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_InterestAndOtherIncome_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Interest and Other Income</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_InterestAndOtherIncome_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Interest and Other Income, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OtherComprehensiveIncomeLossNetOfTaxPeriodIncreaseDecreaseAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Other Comprehensive Income (Loss), Net of Tax [Abstract]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OtherComprehensiveIncomeLossNetOfTaxPeriodIncreaseDecreaseAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Other comprehensive (loss) income, net of tax:</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_LongTermDebtFairValue_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Long-term borrowings</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_LongTermDebtFairValue_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Long-Term Debt, Fair Value</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_FinancingReceivables30To89DaysPastDueMember_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Financing Receivables 30 To 89 Days Past Due</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_FinancingReceivables30To89DaysPastDueMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Financing Receivables 30 To 89 Days Past Due [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_FinancingReceivables30To89DaysPastDueMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">30-89 Days Past Due</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodNetOfTax_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Total reclassified for the period</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodNetOfTax_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodNetOfTax_lbl" xlink:role="http://www.xbrl.org/2009/role/negatedTotalLabel">Total reclassified for the period</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodNetOfTax_lbl" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Reclassification, Net of tax amount</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodNetOfTax_lbl" xlink:role="http://www.xbrl.org/2009/role/negatedLabel">Amounts reclassified from accumulated other comprehensive income</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodNetOfTax_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Total reclassified for the period</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_OtherLiabilitiesMiscellaneous_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Other liabilities miscellaneous.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_OtherLiabilitiesMiscellaneous_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Other Liabilities Miscellaneous</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_OtherLiabilitiesMiscellaneous_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Other</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_InterestExpenseOperating_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Interest expense</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_InterestExpenseOperating_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Interest Expense, Operating</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_InterestExpenseOperating_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Total interest expense</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Table]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Fair Value Measurement Inputs and Valuation Techniques [Table]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_InterestIncomeExpenseAfterProvisionForLoanLoss_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Interest Income (Expense), after Provision for Loan Loss</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_InterestIncomeExpenseAfterProvisionForLoanLoss_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Net interest income after provision for credit losses</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_FraudulentActivityPolicyTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Fraudulent Activity Policy.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_FraudulentActivityPolicyTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Fraudulent Activity Policy [ Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_FraudulentActivityPolicyTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Fraudulent Activity</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Antidilutive Securities</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Antidilutive Securities [Axis]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_BasisOfPresentationAndSignificantAccountingPoliciesTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Basis of Presentation and Summary of Significant Accounting Policies</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_BasisOfPresentationAndSignificantAccountingPoliciesTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Basis of Presentation and Significant Accounting Policies [Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_ConstructionMortgageMember_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Construction mortgage.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_ConstructionMortgageMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Construction Mortgage [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_ConstructionMortgageMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Construction [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DerivativeLiabilityNotionalAmount_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Derivative Liability, Notional Amount</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ProceedsFromSaleOfAvailableForSaleSecuritiesDebt_lbl" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Proceeds from sales</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ProceedsFromSaleOfAvailableForSaleSecuritiesDebt_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Proceeds from Sale of Debt Securities, Available-for-Sale</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ProceedsFromSaleOfAvailableForSaleSecuritiesDebt_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Proceeds from sales of securities available for sale</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_CommitmentsAndContingenciesTable_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Commitments And Contingencies [Table]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_CommitmentsAndContingenciesTable_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Commitments And Contingencies [Table]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_CommitmentsAndContingenciesTable_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Commitments and contingencies.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AvailableforsaleSecuritiesMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Available for Sale Securities [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AvailableforsaleSecuritiesMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Available-for-Sale Securities [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AccumulatedOtherComprehensiveIncomeMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">AOCI Attributable to Parent [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AccumulatedOtherComprehensiveIncomeMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Accumulated Other Comprehensive Loss [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AccumulatedOtherComprehensiveIncomeMember_lbl" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Accumulated Other Comprehensive (Loss) Income [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DerivativeLiabilities_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Derivative instruments, liabilities</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DerivativeLiabilities_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Derivative Liability</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DerivativeLiabilities_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Derivative Liability, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Finite-Lived Intangible Assets, Major Class Name [Domain]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Finite-Lived Intangible Assets, Major Class Name</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_TreasuryStockCommonShares_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Treasury Stock, Common, Shares</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_TreasuryStockCommonShares_lbl" xlink:role="http://www.xbrl.org/2003/role/periodStartLabel">Treasury stock, beginning balance</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_TreasuryStockCommonShares_lbl" xlink:role="http://www.xbrl.org/2003/role/periodEndLabel">Treasury stock, ending balance</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_TreasuryStockCommonShares_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Treasury stock, shares</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueInRollingYearFive_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Lessee, Operating Lease, Liability, to be Paid, Rolling Year Five</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueInRollingYearFive_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">2030</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_StockIssuedDuringPeriodSharesTreasuryStockReissued_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Stock awards</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_StockIssuedDuringPeriodSharesTreasuryStockReissued_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Stock Issued During Period, Shares, Treasury Stock Reissued</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseAfterYearFive_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Thereafter</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseAfterYearFive_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Finite-Lived Intangible Asset, Expected Amortization, after Year Five</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PreferredStockValue_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Total preferred equity</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PreferredStockValue_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Preferred Stock, Value, Issued</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PreferredStockValue_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Preferred Stock, Value, Issued, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PreferredStockValue_lbl" xlink:role="http://www.xbrl.org/2003/role/periodStartLabel">Preferred Stock, Value, Issued, Beginning Balance</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PreferredStockValue_lbl" xlink:role="http://www.xbrl.org/2003/role/periodEndLabel">Preferred Stock, Value, Issued, Ending Balance</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeDomain_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Reclassification out of Accumulated Other Comprehensive Income</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeDomain_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Reclassification out of Accumulated Other Comprehensive Income [Domain]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="srt_MinimumMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Minimum [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="srt_MinimumMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Minimum [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_lbl" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Grant date fair value</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Granted, Weighted Average Market Price at Grant Date</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FinancialInstrumentAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Financial Instrument</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FinancialInstrumentAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Financial Instrument [Axis]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DerivativeFairValueOfDerivativeAsset_lbl" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Asset derivatives</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DerivativeFairValueOfDerivativeAsset_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Derivative instruments</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DerivativeFairValueOfDerivativeAsset_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Derivative Asset, Subject to Master Netting Arrangement, before Offset</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DerivativeFairValueOfDerivativeAsset_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Derivative Asset, Fair Value, Gross Asset, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FinancingReceivableOriginatedInFiscalYearBeforeLatestFiscalYear_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Prior Fiscal Year 1</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FinancingReceivableOriginatedInFiscalYearBeforeLatestFiscalYear_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Financing Receivable, Year Two, Originated, Fiscal Year before Current Fiscal Year</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OtherComprehensiveIncomeLossTax_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Other Comprehensive Income (Loss), Tax</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OtherComprehensiveIncomeLossTax_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Other comprehensive income (loss), Tax Effect</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_NonMaturityDepositsFairValueDisclosure_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Non-maturity deposits</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_NonMaturityDepositsFairValueDisclosure_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Non Maturity Deposits Fair Value Disclosure</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_NonMaturityDepositsFairValueDisclosure_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Non-Maturity Deposits Fair Value Disclosure</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_CollateralizedMortgageBackedSecuritiesFederalNationalMortgageAssociationCertificatesAndObligationsFnmaMember_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Collateralized Mortgage-Backed Securities Federal National Mortgage Association Certificates and Obligations (FNMA).</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_CollateralizedMortgageBackedSecuritiesFederalNationalMortgageAssociationCertificatesAndObligationsFnmaMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Collateralized Mortgage-Backed Securities Federal National Mortgage Association Certificates and Obligations (FNMA) [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_ForegoneInterestOnNonAccrualLoans_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Foregone interest on non accrual loans</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_ForegoneInterestOnNonAccrualLoans_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Foregone Interest on Non Accrual Loans</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_ForegoneInterestOnNonAccrualLoans_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Foregone interest on non accrual loans.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AmortizationOfIntangibleAssets_lbl" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Amortization expense during the year</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AmortizationOfIntangibleAssets_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Amortization of intangibles</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AmortizationOfIntangibleAssets_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Amortization of Intangible Assets</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AmortizationOfIntangibleAssets_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Amortization of Intangible Assets, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DeferredTaxAssetsUnrealizedLossesOnAvailableforSaleSecuritiesGross_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Deferred Tax Asset, Debt Securities, Available-for-Sale, Unrealized Loss</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DeferredTaxAssetsUnrealizedLossesOnAvailableforSaleSecuritiesGross_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Pre-tax loss</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FairValueInputsLevel3Member_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Level 3 Inputs [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FairValueInputsLevel3Member_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Fair Value, Inputs, Level 3 [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FairValueMeasurementsNonrecurringMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Measured On A Nonrecurring Basis [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FairValueMeasurementsNonrecurringMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Fair Value, Nonrecurring [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_SegmentReportingAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Segment Reporting [Abstract]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_CollateralDependentLoans_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Collateral dependent loans</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_CollateralDependentLoans_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Collateral Dependent Loans</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_CollateralDependentLoans_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Collateral dependent loans.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PreferredStockDividendsPerShareDeclared_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Preferred stock dividends per share, declared</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PreferredStockDividendsPerShareDeclared_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Preferred Stock, Dividends Per Share, Declared</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AccumulatedGainLossNetCashFlowHedgeParentMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Hedging Derivative Instruments [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AccumulatedGainLossNetCashFlowHedgeParentMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Accumulated Gain (Loss), Net, Cash Flow Hedge, Parent [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OtherAssetsMiscellaneous_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Other Assets, Miscellaneous, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OtherAssetsMiscellaneous_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Other</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OtherAssetsMiscellaneous_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Other Assets, Miscellaneous</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_SubleaseIncome_lbl" xlink:role="http://www.xbrl.org/2009/role/negatedLabel">Sublease income</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_SubleaseIncome_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Sublease Income</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ScheduleOfAccountsNotesLoansAndFinancingReceivableTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Loan Portfolio</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ScheduleOfAccountsNotesLoansAndFinancingReceivableTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Schedule of Accounts, Notes, Loans and Financing Receivable [Table Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_InterestExpenseAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Interest expense:</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_InterestExpenseAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Interest Expense, Operating and Nonoperating [Abstract]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OtherLiabilitiesAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Other Liabilities [Abstract]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OtherLiabilitiesAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Other Liabilities:</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_InternallyRatedHeldToMaturitySecurities_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Internally rated held-to-maturity securities.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_InternallyRatedHeldToMaturitySecurities_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Internally rated held-to-maturity securities</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_InternallyRatedHeldToMaturitySecurities_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Internally Rated Held To Maturity Securities</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_InterestRateContractMember_lbl" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Interest Rate Products [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_InterestRateContractMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Interest Rate Contract [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_InterestRateContractMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Interest Rate Swaps / Products [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_CommitmentsAndContingencies_lbl" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Off-balance sheet commitments</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_CommitmentsAndContingencies_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Commitments and Contingencies</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DefinedBenefitPlanServiceCost_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Service cost</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DefinedBenefitPlanServiceCost_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Defined Benefit Plan, Service Cost</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeTable_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Reclassification Out Of Accumulated Other Comprehensive Income [Table]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeTable_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Reclassification out of Accumulated Other Comprehensive Income [Table]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_CollateralDependentLoanWithSpecificReserve_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Collateral dependent loan with specific reserve</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_CollateralDependentLoanWithSpecificReserve_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Collateral Dependent Loan With Specific Reserve</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_CollateralDependentLoanWithSpecificReserve_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Collateral dependent loan with specific reserve.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OperatingLeaseLiability_lbl" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Present value of net future minimum operating lease payments</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OperatingLeaseLiability_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Operating Lease, Liability</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OperatingLeaseLiability_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Operating Lease, Liability, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OperatingLeaseLiability_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Operating lease right of use obligations</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PreferredStockDividendRatePercentage_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Preferred stock, dividend percentage</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PreferredStockDividendRatePercentage_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Preferred Stock, Dividend Rate, Percentage</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="srt_ScenarioForecastMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Forecast [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="srt_ScenarioForecastMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Forecast [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ShortTermBorrowings_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Short-term borrowings</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ShortTermBorrowings_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Short-Term Debt</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ShortTermBorrowings_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Short-term Debt, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ScheduleOfGoodwillTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Changes in Carrying Amount of Goodwill</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ScheduleOfGoodwillTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Schedule of Goodwill [Table Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_USTreasuryBillSecuritiesMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">US Treasury Bill Securities [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_USTreasuryBillSecuritiesMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">U.S. Treasury Bills [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ProvisionForOtherCreditLosses_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Provision for Other Credit Losses</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ProvisionForOtherCreditLosses_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Provision for credit loss</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_InterestRateSwapTransactionThreeMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Interest Rate Swap Transaction Three [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_InterestRateSwapTransactionThreeMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Interest Rate Swap Transaction Three [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_InterestRateSwapTransactionThreeMember_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Interest rate swap transaction three.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FinancingReceivableImpairedLineItems_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Financing Receivable, Impaired [Line Items]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FinancingReceivableImpairedLineItems_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Financing Receivable, Impaired [Line Items]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_CurrentMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Current</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_CurrentMember_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Current.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_CurrentMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Current [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_InterestAndDividendIncomeOperating_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Total interest income</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_InterestAndDividendIncomeOperating_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Interest and Dividend Income, Operating</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_InterestAndDividendIncomeOperating_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Interest income</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FinancingReceivableOriginatedFiveOrMoreYearsBeforeLatestFiscalYear_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Prior</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FinancingReceivableOriginatedFiveOrMoreYearsBeforeLatestFiscalYear_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Financing Receivable, Originated, More than Five Years before Current Fiscal Year</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AssetsHeldForSaleLongLivedFairValueDisclosure_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Long-lived assets held for sale</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AssetsHeldForSaleLongLivedFairValueDisclosure_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Long-Lived Asset, Held-for-Sale, Fair Value Disclosure</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_InterestIncomeExpenseNet_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Net interest income</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_InterestIncomeExpenseNet_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Interest Income (Expense), Operating</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_InterestIncomeExpenseNet_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Interest income</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_InterestIncomeExpenseNet_lbl" xlink:role="http://www.xbrl.org/2009/role/negatedLabel">Interest income</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_InterestIncomeExpenseNet_lbl" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Net interest income (expense)</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ProfitLoss_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Net income</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ProfitLoss_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Net Income (Loss), Including Portion Attributable to Noncontrolling Interest</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ProfitLoss_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Net Income (Loss), Including Portion Attributable to Noncontrolling Interest, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_NotesReceivableGross_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Principal Amount Outstanding</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_NotesReceivableGross_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Total Loans</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_NotesReceivableGross_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Investment securities, past due</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_NotesReceivableGross_lbl" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Total Loans</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_HeldToMaturitySecurities_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Securities held to maturity, Amortized Cost</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_HeldToMaturitySecurities_lbl" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Securities held to maturity, Amortized Cost</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_HeldToMaturitySecurities_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Debt Securities, Held-to-Maturity, Amortized Cost, before Allowance for Credit Loss</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FinancingReceivableRecordedInvestment90DaysPastDueAndStillAccruing_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Past due greater than 90 days and still accruing interest</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FinancingReceivableRecordedInvestment90DaysPastDueAndStillAccruing_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Financing Receivable, 90 Days or More Past Due, Still Accruing</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ReconciliationOfAssetsFromSegmentToConsolidatedTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Reconciliation of Assets from Segment to Consolidated [Table Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ReconciliationOfAssetsFromSegmentToConsolidatedTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Balance Sheet Information of Segment Assets</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_CashPaidForAmountsIncludedInMeasurementOfLeaseLiabilitiesAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Cash paid for amounts included in the measurement of lease liabilities:</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_CashPaidForAmountsIncludedInMeasurementOfLeaseLiabilitiesAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Cash Paid For Amounts Included In Measurement Of Lease Liabilities [Abstract]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_CashPaidForAmountsIncludedInMeasurementOfLeaseLiabilitiesAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Cash paid for amounts included in measurement of lease liabilities.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_WeightedAverageNumberOfSharesOutstandingBasic_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Total basic weighted average common shares outstanding</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_WeightedAverageNumberOfSharesOutstandingBasic_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Weighted Average Number of Shares Outstanding, Basic</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="srt_StatementScenarioAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Scenario</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="srt_StatementScenarioAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Scenario [Axis]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_CollateralizedMortgageObligationsGovernmentNationalMortgageAssociationCertificatesAndObligationsGnmaMember_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Collateralized mortgage obligations government national mortgage association certificates and obligations Gnma.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_CollateralizedMortgageObligationsGovernmentNationalMortgageAssociationCertificatesAndObligationsGnmaMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Collateralized Mortgage Obligations Government National Mortgage Association Certificates And Obligations Gnma [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_CollateralizedMortgageObligationsGovernmentNationalMortgageAssociationCertificatesAndObligationsGnmaMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Collateralized Mortgage Obligations Government National Mortgage Association Certificates And Obligations (GNMA) [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Schedule Of Share Based Compensation Arrangements By Share Based Payment Award [Table]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Schedule of Share-Based Compensation Arrangements by Share-Based Payment Award [Table]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Securities available for sale, 12 months or longer, Unrealized Losses</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Debt Securities, Available-for-Sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_InterestPayableCurrentAndNoncurrent_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Interest Payable</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_InterestPayableCurrentAndNoncurrent_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Accrued interest expense</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_LoansReceivableFairValueDisclosure_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Loans</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_LoansReceivableFairValueDisclosure_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Loans Receivable, Fair Value Disclosure</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_LongTermDebt_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Long-Term Debt</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_LongTermDebt_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Long-term Debt, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_LongTermDebt_lbl" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Long-term borrowings</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_LongTermDebt_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Long-term borrowings, net of issuance costs of $1,306 and $1,347, respectively</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Share-based compensation</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue_lbl" xlink:role="http://www.xbrl.org/2003/role/label">APIC, Share-Based Payment Arrangement, Increase for Cost Recognition</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">APIC, Share-based Payment Arrangement, Increase for Cost Recognition, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_CollateralizedMortgageObligationsMortgageBackedSecuritiesIssuedByPrivateEnterprisesMember_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Collateralized Mortgage Obligations Mortgage-Backed Securities, Issued by Private Enterprises.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_CollateralizedMortgageObligationsMortgageBackedSecuritiesIssuedByPrivateEnterprisesMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Collateralized Mortgage Obligations Mortgage-Backed Securities, Issued by Private Enterprises [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_StockholdersEquity_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Total shareholders&#8217; equity</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_StockholdersEquity_lbl" xlink:role="http://www.xbrl.org/2003/role/periodStartLabel">Balance</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_StockholdersEquity_lbl" xlink:role="http://www.xbrl.org/2003/role/periodEndLabel">Balance</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_StockholdersEquity_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Equity, Attributable to Parent</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PreferredStockParOrStatedValuePerShare_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Preferred stock, par value</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PreferredStockParOrStatedValuePerShare_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Preferred Stock, Par or Stated Value Per Share</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_BasisOfAccountingPolicyPolicyTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Basis of Presentation</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_BasisOfAccountingPolicyPolicyTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Basis of Accounting, Policy [Policy Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PrincipalAmountOutstandingOfLoansHeldInPortfolio_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Loan, Held-in-Portfolio, Principal Outstanding</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PrincipalAmountOutstandingOfLoansHeldInPortfolio_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Principal Amount Outstanding</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PrincipalAmountOutstandingOfLoansHeldInPortfolio_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Principal Amount Outstanding</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_StatementOfStockholdersEquityAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Statement of Stockholders' Equity [Abstract]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_CollateralizedMortgageObligationsFederalHomeLoanMortgageCorporationCertificatesAndObligationsFhlmcMember_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Collateralized Mortgage Obligations Federal Home Loan Mortgage Corporation Certificates and Obligations (FHLMC).</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_CollateralizedMortgageObligationsFederalHomeLoanMortgageCorporationCertificatesAndObligationsFhlmcMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Collateralized Mortgage Obligations Federal Home Loan Mortgage Corporation Certificates and Obligations (FHLMC) [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_HeldToMaturitySecuritiesAccumulatedUnrecognizedHoldingLoss_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Securities held to maturity, Unrealized Losses</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_HeldToMaturitySecuritiesAccumulatedUnrecognizedHoldingLoss_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Debt Securities, Held-to-Maturity, Accumulated Unrecognized Loss</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OtherComprehensiveIncomeLossBeforeReclassificationsTax_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Other comprehensive income (loss), before Reclassifications, Tax Effect</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OtherComprehensiveIncomeLossBeforeReclassificationsTax_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Other Comprehensive Income (Loss) before Reclassifications, Tax</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OtherComprehensiveIncomeLossBeforeReclassificationsTax_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Other Comprehensive Income (Loss) before Reclassifications, Tax, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseRemainderOfFiscalYear_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Finite-Lived Intangible Asset, Expected Amortization, Remainder of Fiscal Year</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseRemainderOfFiscalYear_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">2026 (remainder of year)</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_TransferToInvestments_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Transfer to Investments</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_TransferToInvestments_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Transfer of premises and equipment to assets held for sale</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ValuationTechniqueDomain_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Valuation Approach and Technique</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ValuationTechniqueDomain_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Valuation Approach and Technique [Domain]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_UseOfEstimates_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Use of Estimates</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_UseOfEstimates_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Use of Estimates, Policy [Policy Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_InternalCreditAssessmentDomain_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Internal Credit Assessment</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_InternalCreditAssessmentDomain_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Internal Credit Assessment [Domain]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_TreasuryStockCommonMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Treasury Stock, Common [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_TreasuryStockCommonMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Treasury Stock [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_AllowanceForCreditLossesAmortizedCost_lbl" xlink:role="http://www.xbrl.org/2009/role/negatedLabel">Allowance for credit losses, Amortized Cost</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_AllowanceForCreditLossesAmortizedCost_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Allowance For Credit Losses Amortized Cost</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_AllowanceForCreditLossesAmortizedCost_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Allowance for credit losses, amortized cost.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FinancingReceivableAllowanceForCreditLosses_lbl" xlink:role="http://www.xbrl.org/2003/role/periodStartLabel">Beginning balance</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FinancingReceivableAllowanceForCreditLosses_lbl" xlink:role="http://www.xbrl.org/2003/role/periodEndLabel">Ending balance</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FinancingReceivableAllowanceForCreditLosses_lbl" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Loans, allowance for credit losses</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FinancingReceivableAllowanceForCreditLosses_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Financing Receivable, Allowance for Credit Loss</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FinancingReceivableAllowanceForCreditLosses_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Allowance for credit losses</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FinancingReceivableAllowanceForCreditLosses_lbl" xlink:role="http://www.xbrl.org/2009/role/negatedLabel">Allowance for credit losses-loans</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FairValueDisclosuresTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Fair Value Measurements</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FairValueDisclosuresTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Fair Value Disclosures [Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PaymentsToAcquireHeldToMaturitySecurities_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Payments to Acquire Held-to-Maturity Securities</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PaymentsToAcquireHeldToMaturitySecurities_lbl" xlink:role="http://www.xbrl.org/2009/role/negatedLabel">Purchases of held to maturity securities</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Pension And Post-Retirement Obligations [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Accumulated Defined Benefit Plans Adjustment Attributable to Parent [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ExtendedMaturityMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Extended Maturity [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ExtendedMaturityMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Extended Maturity [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_MeasurementInputDiscountRateMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Discount Rate [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_MeasurementInputDiscountRateMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Measurement Input, Discount Rate [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosureAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Derivative Instruments and Hedging Activities Disclosure [Abstract]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_SegmentReportingCodmIndividualTitleAndPositionOrGroupOrCommitteeNameExtensibleEnumeration_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Segment Reporting, CODM, Individual Title and Position or Group Name [Extensible Enumeration]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueNextRollingTwelveMonths_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Lessee, Operating Lease, Liability, to be Paid, Next Rolling 12 Months</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueNextRollingTwelveMonths_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">2026</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_IncreaseDecreaseInOtherOperatingAssets_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Increase (Decrease) in Other Operating Assets</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_IncreaseDecreaseInOtherOperatingAssets_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Increase (Decrease) in Other Operating Assets, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_IncreaseDecreaseInOtherOperatingAssets_lbl" xlink:role="http://www.xbrl.org/2009/role/negatedLabel">Decrease in other assets</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_IncreaseDecreaseInOtherOperatingAssets_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Decrease in other assets</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Fair Value Assets And Liabilities Measured On Recurring and Nonrecurring Basis [Line Items]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterTenYearsFairValue_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Debt securities available for sale, Due after ten years, Fair Value</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterTenYearsFairValue_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Debt Securities, Available-for-Sale, Fair Value, Maturity, Allocated and Single Maturity Date, after Year 10</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ScheduleOfInvestmentsLineItems_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Schedule Of Investments [Line Items]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ScheduleOfInvestmentsLineItems_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Schedule of Investments [Line Items]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_LoanRestructuringModificationAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Loan Restructuring Modification</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_LoanRestructuringModificationAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Loan Restructuring Modification [Axis]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_TroubledDebtRestructuringsOnFinancingReceivablesPerformanceOfLoansTableTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Troubled debt restructurings on financing receivables performance of loans.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_TroubledDebtRestructuringsOnFinancingReceivablesPerformanceOfLoansTableTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Troubled Debt Restructurings On Financing Receivables Performance of Loans [Table Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_TroubledDebtRestructuringsOnFinancingReceivablesPerformanceOfLoansTableTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Performance of Loans that are Modified to Borrowers Experiencing Financial Difficulty</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_OtherNoninterestExpensesMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Other Noninterest Expense [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_OtherNoninterestExpensesMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Other Noninterest Expenses [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_OtherNoninterestExpensesMember_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Other noninterest expenses that are not performance, advisory, custodian, directors' fees, offering costs, commission expenses or printing and fulfillment costs and are not covered in any other noninterest expense category.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_TreasuryStockValue_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Treasury Stock, Value</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_TreasuryStockValue_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Treasury Stock, Value, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_TreasuryStockValue_lbl" xlink:role="http://www.xbrl.org/2003/role/periodStartLabel">Treasury Stock, Value, Beginning Balance</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_TreasuryStockValue_lbl" xlink:role="http://www.xbrl.org/2003/role/periodEndLabel">Treasury Stock, Value, Ending Balance</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_TreasuryStockValue_lbl" xlink:role="http://www.xbrl.org/2009/role/negatedLabel">Treasury stock, at cost; 993,196 and 902,149 shares, respectively</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FinancingReceivableOriginatedInCurrentFiscalYear_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Current Fiscal Year</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FinancingReceivableOriginatedInCurrentFiscalYear_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Financing Receivable, Year One, Originated, Current Fiscal Year</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_ScheduleOfCreditLossExpenseBenefitForUnfundedCommitmentsTableTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Schedule of credit loss expense benefit for unfunded commitments.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_ScheduleOfCreditLossExpenseBenefitForUnfundedCommitmentsTableTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Schedule of Credit Loss Expense Benefit for Unfunded Commitments [Table Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_ScheduleOfCreditLossExpenseBenefitForUnfundedCommitmentsTableTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Schedule of Credit Loss for Unfunded Commitments</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_CashAndDueFromBanks_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Cash and due from banks</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_CashAndDueFromBanks_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Cash and Due from Banks</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_CashAndDueFromBanks_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Cash and Due from Banks, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PastDueFinancingReceivablesTableTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Recorded Investment by Loan Class in Current and Nonaccrual Loans</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PastDueFinancingReceivablesTableTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Financing Receivable, Past Due [Table Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_EntityAddressCityOrTown_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Entity Address, City or Town</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_EntityAddressCityOrTown_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Entity Address, City or Town</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_WeightedAverageNumberOfSharesTreasuryStock_lbl" xlink:role="http://www.xbrl.org/2009/role/negatedLabel">Treasury shares</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_WeightedAverageNumberOfSharesTreasuryStock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Weighted Average Number of Shares, Treasury Stock</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_NumberOfReportableSegments_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Number of reportable segments</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_NumberOfReportableSegments_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Number of Reportable Segments</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_LitigationSettlementInterest_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Provision for litigation settlement</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_LitigationSettlementInterest_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Litigation Settlement Interest</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_SecurityExchangeName_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Security Exchange Name</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_SecurityExchangeName_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Security Exchange Name</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_GovernmentNationalMortgageAssociationCertificatesAndObligationsGNMAMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Government National Mortgage Association Certificates and Obligations (GNMA) [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_GovernmentNationalMortgageAssociationCertificatesAndObligationsGNMAMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Government National Mortgage Association [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_InterestExpenseDeposits_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Deposits</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_InterestExpenseDeposits_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Interest Expense, Deposits</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_InterestExpenseDeposits_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Interest Expense, Deposits, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_NoninterestExpenseAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Noninterest expense:</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_NoninterestExpenseAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Noninterest Expense [Abstract]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_OperationalAccountingAndReportingImpactsRelatedToCovidPandemicPolicyTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Operational, Accounting and Reporting Impacts Related to the COVID-19 Pandemic</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_OperationalAccountingAndReportingImpactsRelatedToCovidPandemicPolicyTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Operational Accounting And Reporting Impacts Related To Covid Pandemic Policy [Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_OperationalAccountingAndReportingImpactsRelatedToCovidPandemicPolicyTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Operational accounting and reporting impacts related to Covid pandemic.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Income before income taxes</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Income before income tax benefit</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest_lbl" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Income before income taxes</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_PerformanceShareUnitsMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">PSUs [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_PerformanceShareUnitsMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Performance Share Units [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_PerformanceShareUnitsMember_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Performance Share Units [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DepositsSavingsDeposits_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Savings and money market</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DepositsSavingsDeposits_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Deposits, Savings Deposits</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_GainLossOnSaleOfOtherAssets_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Gain (Loss) on Disposition of Other Assets</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_GainLossOnSaleOfOtherAssets_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Net (loss) gain on sale and disposal of other assets</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_GainLossOnSaleOfOtherAssets_lbl" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Net loss on other assets</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_GainLossOnSaleOfOtherAssets_lbl" xlink:role="http://www.xbrl.org/2009/role/negatedLabel">Net loss on other assets</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_ConsumerIndirectMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Consumer Indirect [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_ConsumerIndirectMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Consumer Indirect [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_ConsumerIndirectMember_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Consumer Indirect [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_MeasurementInputTypeDomain_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Measurement Input Type</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_MeasurementInputTypeDomain_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Measurement Input Type [Domain]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AccumulatedDefinedBenefitPlansAdjustmentNetPriorServiceIncludingPortionAttributableToNoncontrollingInterestMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Accumulated Defined Benefit Plans Adjustment, Net Prior Service Including Portion Attributable to Noncontrolling Interest [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AccumulatedDefinedBenefitPlansAdjustmentNetPriorServiceIncludingPortionAttributableToNoncontrollingInterestMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Accumulated Defined Benefit Plans Adjustment, Net Prior Service Including Portion Attributable to Noncontrolling Interest [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AntidilutiveSecuritiesNameDomain_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Antidilutive Securities, Name</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AntidilutiveSecuritiesNameDomain_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Antidilutive Securities, Name [Domain]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_StockholdersEquityNoteAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Stockholders' Equity Note [Abstract]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DepositsAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Deposits:</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DepositsAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Deposits [Abstract]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_OwnerOccupiedMortgageMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Owner Occupied [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_OwnerOccupiedMortgageMember_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Owner occupied mortgage.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_OwnerOccupiedMortgageMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Owner Occupied Mortgage [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FinancialAssetNotPastDueMember_lbl" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Total Loans [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FinancialAssetNotPastDueMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Financial Asset, Not Past Due [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FinancialAssetNotPastDueMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Current [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_ScheduleOfClassificationOfRightOfUseAssetsAndLeaseLiabilitiesTableTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Summary of Classification of Right of Use Assets and Lease Liabilities</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_ScheduleOfClassificationOfRightOfUseAssetsAndLeaseLiabilitiesTableTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Schedule Of Classification Of Right Of Use Assets And Lease Liabilities Table [Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_ScheduleOfClassificationOfRightOfUseAssetsAndLeaseLiabilitiesTableTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Schedule of classification of right of use assets and lease liabilities.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_CoreDepositsMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Core Deposits [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_CoreDepositsMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Core Deposits [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_InterestPaidNet_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Interest Paid, Excluding Capitalized Interest, Operating Activity</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_InterestPaidNet_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Cash paid for interest</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AccumulatedGainLossCashFlowHedgeIncludingNoncontrollingInterestMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Accumulated Net Gain (Loss) from Cash Flow Hedges Including Portion Attributable to Noncontrolling Interest [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AccumulatedGainLossCashFlowHedgeIncludingNoncontrollingInterestMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Accumulated Gain (Loss), Cash Flow Hedge, Including Noncontrolling Interest [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FairValueByMeasurementBasisAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Estimated Fair Value [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FairValueByMeasurementBasisAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Measurement Basis [Axis]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="srt_RangeMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Statistical Measurement</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="srt_RangeMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Statistical Measurement [Domain]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_DocumentPeriodEndDate_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Document Period End Date</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_DocumentPeriodEndDate_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Document Period End Date</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FairValueMeasurementsFairValueHierarchyDomain_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Fair Value Hierarchy and NAV</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FairValueMeasurementsFairValueHierarchyDomain_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Fair Value Hierarchy and NAV [Domain]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_CommitmentsAndContingenciesLineItems_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Commitments And Contingencies [Line Items]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_CommitmentsAndContingenciesLineItems_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Commitments And Contingencies [Line Items]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_CommitmentsAndContingenciesLineItems_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Commitments and contingencies.</link:label>
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          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_Higher-YieldingAgencyWrappedInvestmentsMember_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Higher-yielding agency wrapped investments.</link:label>
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          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_LongLivedAssetsHeldForSaleMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Long-lived Assets Held for Sale [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_LongLivedAssetsHeldForSaleMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Long Lived Assets Held For Sale [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_LongLivedAssetsHeldForSaleMember_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Long-lived assets held for sale.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_StatementOfFinancialPositionAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Statement of Financial Position [Abstract]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_RestrictedStockUnitsRSUMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">RSUs [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_RestrictedStockUnitsRSUMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Restricted Stock Units (RSUs) [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="srt_CumulativeEffectPeriodOfAdoptionAdjustmentMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Cumulative-Effect Adjustment [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="srt_CumulativeEffectPeriodOfAdoptionAdjustmentMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Cumulative Effect, Period of Adoption, Adjustment [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DebtSecuritiesAvailableForSaleRealizedLoss_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Debt Securities, Available-for-Sale, Realized Loss</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DebtSecuritiesAvailableForSaleRealizedLoss_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Gross realized losses</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_InvestmentSecuritiesInUnrealizedLossPositionsLessThanTwelveMonthsQualitativeDisclosureNumberOfPositions_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Number of security positions, unrealized loss position for less than 12 months</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_InvestmentSecuritiesInUnrealizedLossPositionsLessThanTwelveMonthsQualitativeDisclosureNumberOfPositions_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Investment Securities In Unrealized Loss Positions Less Than Twelve Months Qualitative Disclosure Number Of Positions</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_InvestmentSecuritiesInUnrealizedLossPositionsLessThanTwelveMonthsQualitativeDisclosureNumberOfPositions_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Disclosure regarding factors used to determine that the impairment of securities not categorized as either held-to-maturity securities or trading securities (hence equal to available for sale securities) where cost exceeds fair value is not an other than temporary impairment (OTTI). This item contains disclosure of the number of investment positions in the available-for-sale investments determined to be temporarily impaired for less than twelve months.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Schedule Of Antidilutive Securities Excluded From Computation Of Earnings Per Share [Table]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Antidilutive Security, Excluded EPS Calculation [Table]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Reclassification out of Accumulated Other Comprehensive (Loss) Income [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Reclassification out of Accumulated Other Comprehensive Income [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_StatementClassOfStockAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Class of Stock</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_StatementClassOfStockAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Class of Stock [Axis]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_NoninterestIncomeInvestmentsInLimitedPartnerships_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Investments in limited partnerships</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_NoninterestIncomeInvestmentsInLimitedPartnerships_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Noninterest Income Investments In Limited Partnerships</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_NoninterestIncomeInvestmentsInLimitedPartnerships_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Noninterest income from investments in limited partnerships.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_FairValueAssetsLevel1ToLevel2TransferAmount_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Level 1 to Level 2 transfers, assets amount</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_FairValueAssetsLevel1ToLevel2TransferAmount_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Fair Value, Assets, Level 1 to Level 2 Transfer, Amount</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_FairValueAssetsLevel1ToLevel2TransferAmount_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Amount of transfers of assets measured on a recurring basis out of Level 1 of the fair value hierarchy into Level 2.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_FinancingReceivableAllowanceForLoanLossesProvisionCredit_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Financing Receivable Allowance For Loan Losses Provision Credit</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_FinancingReceivableAllowanceForLoanLossesProvisionCredit_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Financing receivable allowance for loan losses, provision (credit).</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_FinancingReceivableAllowanceForLoanLossesProvisionCredit_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Provision (benefit)</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_InvestmentSecuritiesContinuousUnrealizedLossPositionTwelveMonthsOrLongerFairValue_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Investment Securities Continuous Unrealized Loss Position Twelve Months Or Longer Fair Value</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_InvestmentSecuritiesContinuousUnrealizedLossPositionTwelveMonthsOrLongerFairValue_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">This item represents the fair value of securities that have been in a continuous unrealized loss position for twelve months or longer.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_InvestmentSecuritiesContinuousUnrealizedLossPositionTwelveMonthsOrLongerFairValue_lbl" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Securities, 12 months or longer, Fair Value</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_InvestmentSecuritiesContinuousUnrealizedLossPositionTwelveMonthsOrLongerFairValue_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Total AFS debt securities with unrealized losses, 12 months or longer, Fair Value</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_NondesignatedMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Derivatives Not Designated as Hedging Instruments [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_NondesignatedMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Not Designated as Hedging Instrument [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FinancingReceivablesPeriodPastDueDomain_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Financial Asset, Period Past Due</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FinancingReceivablesPeriodPastDueDomain_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Financial Asset, Aging [Domain]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_IncreaseDecreaseInDeposits_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Increase (Decrease) in Deposits</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_IncreaseDecreaseInDeposits_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Increase (Decrease) in Deposits, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_IncreaseDecreaseInDeposits_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Net increase in deposits</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FairValuesDerivativesBalanceSheetLocationByDerivativeContractTypeByHedgingDesignationTable_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Fair Values Derivatives Balance Sheet Location By Derivative Contract Type By Hedging Designation [Table]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FairValuesDerivativesBalanceSheetLocationByDerivativeContractTypeByHedgingDesignationTable_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Fair Values Derivatives, Balance Sheet Location, by Derivative Contract Type [Table]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_Liabilities_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Total liabilities</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_Liabilities_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Liabilities</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Financial Instruments</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Financial Instruments [Domain]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DerivativeLiabilityCollateralRightToReclaimCashOffset_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Obligations secured with cash</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DerivativeLiabilityCollateralRightToReclaimCashOffset_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Derivative Liability, Subject to Master Netting Arrangement, Collateral, Right to Reclaim Cash Offset</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ScheduleOfFairValueOffBalanceSheetRisksTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Off-Balance Sheet Commitments</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ScheduleOfFairValueOffBalanceSheetRisksTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Schedule of Fair Value, off-Balance-Sheet Risks [Table Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_HeldToMaturitySecuritiesDebtMaturitiesWithinOneYearNetCarryingAmount_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Debt securities held to maturity, Due in one year or less, Amortized Cost</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_HeldToMaturitySecuritiesDebtMaturitiesWithinOneYearNetCarryingAmount_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Debt Securities, Held-to-Maturity, Amortized Cost, after Allowance for Credit Loss, Maturity, Allocated and Single Maturity Date, Year One</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_HeldToMaturitySecuritiesDebtMaturitiesWithinOneYearFairValue_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Debt securities held to maturity, Due in one year or less, Fair Value</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_HeldToMaturitySecuritiesDebtMaturitiesWithinOneYearFairValue_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Debt Securities, Held-to-Maturity, Fair Value, Maturity, Allocated and Single Maturity Date, Year One</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DefinedBenefitPlanExpectedReturnOnPlanAssets_lbl" xlink:role="http://www.xbrl.org/2009/role/negatedLabel">Expected return on plan assets</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DefinedBenefitPlanExpectedReturnOnPlanAssets_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Defined Benefit Plan, Expected Return (Loss) on Plan Assets</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DerivativeInstrumentsGainLossLineItems_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Derivative Instruments, Gain (Loss) [Line Items]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DerivativeInstrumentsGainLossLineItems_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Derivative Instruments, Gain (Loss) [Line Items]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FinancingReceivableCreditQualityIndicatorsTableTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Commercial Loan Portfolio Categorized by Internally Assigned Asset Classification</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FinancingReceivableCreditQualityIndicatorsTableTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Financing Receivable Credit Quality Indicators [Table Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_BenefitProvisionForCreditLosses_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">(Benefit) provision for credit losses.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_BenefitProvisionForCreditLosses_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Benefit Provision for Credit Losses</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_BenefitProvisionForCreditLosses_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Provision for credit losses</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ScheduleOfFinancingReceivableTroubledDebtRestructuringsTable_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Financing Receivable, Modified [Table]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_RestrictedStockMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Restricted Stock Awards [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_RestrictedStockMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Restricted Stock [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_RestrictedStockMember_lbl" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">RSAs [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_FinancialReceivablesPercentageOfTotalLoans_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Financial receivables percentage of total loans</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_FinancialReceivablesPercentageOfTotalLoans_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Financial Receivables Percentage of Total Loans</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_FinancialReceivablesPercentageOfTotalLoans_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Percentage of total loans</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FiniteLivedIntangibleAssetsGross_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Gross carrying amount</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FiniteLivedIntangibleAssetsGross_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Finite-Lived Intangible Assets, Gross</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FiniteLivedIntangibleAssetsGross_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Finite-Lived Intangible Assets, Gross, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_InterestRateSwapTransactionOneMember_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Interest rate swap transaction one.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_InterestRateSwapTransactionOneMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Interest Rate Swap Transaction One [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_InterestRateSwapTransactionOneMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Interest Rate Swap Transaction One [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Securities available for sale, Less than 12 months, Unrealized Losses</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Debt Securities, Available-for-Sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Total diluted weighted average common shares outstanding</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Weighted Average Number of Shares Outstanding, Diluted</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_InterestAndOtherIncomeTableTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Interest and Other Income [Table Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_InterestAndOtherIncomeTableTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Interest and Dividends on Securities</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_EntityFileNumber_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Entity File Number</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_EntityFileNumber_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Securities Act File Number</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_MarketingAndAdvertisingExpense_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Advertising and promotions</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_MarketingAndAdvertisingExpense_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Marketing and Advertising Expense</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_MarketingAndAdvertisingExpense_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Marketing and Advertising Expense, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_DeposiRelatedChargedOffItemsRecoveriesExpense_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Deposi Related Charged Off Items Recoveries Expense</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_DeposiRelatedChargedOffItemsRecoveriesExpense_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Deposit-related charged-off items (recoveries) expense.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_DeposiRelatedChargedOffItemsRecoveriesExpense_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Deposit-related charged-off items expense (recoveries)</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_ScheduleOfCollateralDependentLoansTableTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Summary of Collateral Dependent Loans</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_ScheduleOfCollateralDependentLoansTableTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Schedule Of Collateral Dependent Loans Table [Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_ScheduleOfCollateralDependentLoansTableTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Schedule of collateral dependent loans.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OtherAssets_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Total other assets</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OtherAssets_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Other assets</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OtherAssets_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Other Assets</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OtherAssets_lbl" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Other assets</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ScheduleOfDerivativeInstrumentsGainLossInStatementOfFinancialPerformanceTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Effect of Derivative Instruments on the Income Statement</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ScheduleOfDerivativeInstrumentsGainLossInStatementOfFinancialPerformanceTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Derivative Instruments, Gain (Loss) [Table Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_CoverAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Cover [Abstract]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_MeasurementInputTypeAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Measurement Input Type</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_MeasurementInputTypeAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Measurement Input Type [Axis]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="srt_CumulativeEffectPeriodOfAdoptionAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Cumulative Effect, Period of Adoption</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="srt_CumulativeEffectPeriodOfAdoptionAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Cumulative Effect, Period of Adoption [Axis]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FinancingReceivablesPeriodPastDueAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Financial Asset, Period Past Due</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FinancingReceivablesPeriodPastDueAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Financial Asset, Aging [Axis]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_InvestmentTypeCategorizationMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Investments</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_InvestmentTypeCategorizationMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Investments [Domain]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ReclassificationFromAociCurrentPeriodTax_lbl" xlink:role="http://www.xbrl.org/2009/role/negatedTerseLabel">Reclassification tax</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ReclassificationFromAociCurrentPeriodTax_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Reclassification, Tax Effect</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ReclassificationFromAociCurrentPeriodTax_lbl" xlink:role="http://www.xbrl.org/2009/role/negatedLabel">Reclassification, Tax Effect</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ReclassificationFromAociCurrentPeriodTax_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Reclassification from AOCI, Current Period, Tax</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ReclassificationFromAociCurrentPeriodTax_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Reclassification tax</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ReclassificationFromAociCurrentPeriodTax_lbl" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Reclassification, Tax Effect</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DerivativeGainLossOnDerivativeNet_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Derivative, Gain (Loss) on Derivative, Net</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DerivativeGainLossOnDerivativeNet_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Derivative, Gain (Loss) on Derivative, Net, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DerivativeGainLossOnDerivativeNet_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Income from derivative instruments, net</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DerivativeGainLossOnDerivativeNet_lbl" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Gain (loss) recognized in Statement of Operations</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueAfterRollingYearFive_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Thereafter</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueAfterRollingYearFive_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Lessee, Operating Lease, Liability, to be Paid, after Rolling Year Five</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_HomeEquityMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Residential Real Estate Lines [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_HomeEquityMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Home Equity Line of Credit [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="srt_ScenarioUnspecifiedDomain_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Scenario</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="srt_ScenarioUnspecifiedDomain_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Scenario [Domain]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_MortgagesMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Mortgage Banking [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_MortgagesMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Mortgages [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_SaleOfStockNameOfTransactionDomain_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Sale of Stock [Domain]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_SegmentReportingDisclosureTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Segment Reporting</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_SegmentReportingDisclosureTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Segment Reporting Disclosure [Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FederalHomeLoanBankStockAndFederalReserveBankStock_lbl" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Federal Home Loan Bank ("FHLB") and Federal Reserve Bank ("FRB") stock</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FederalHomeLoanBankStockAndFederalReserveBankStock_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">FHLB and FRB stock</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FederalHomeLoanBankStockAndFederalReserveBankStock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Federal Home Loan Bank Stock and Federal Reserve Bank Stock</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FederalHomeLoanBankStockAndFederalReserveBankStock_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Federal Home Loan Bank Stock and Federal Reserve Bank Stock, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_ProceedsFromSaleOfDebtSecuritiesAvailableForSaleUsedToFundLosses_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Proceeds from Sale of Debt Securities, Available for Sale Used to Fund Losses</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_ProceedsFromSaleOfDebtSecuritiesAvailableForSaleUsedToFundLosses_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Proceeds from sale of debt securities, available for sale used to fund losses.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_ProceedsFromSaleOfDebtSecuritiesAvailableForSaleUsedToFundLosses_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Proceeds from sales used to fund losses</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_InterestRateCashFlowHedgeGainLossToBeReclassifiedDuringNext12MonthsNet_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Interest Rate Cash Flow Hedge Gain (Loss) to be Reclassified During Next 12 Months, Net</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_InterestRateCashFlowHedgeGainLossToBeReclassifiedDuringNext12MonthsNet_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Estimated reclassification to interest expense during next twelve months</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_GainLossOnTaxCreditInvestments_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Gain Loss On Tax Credit Investments</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_GainLossOnTaxCreditInvestments_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Gain (loss) on tax credit investments.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_GainLossOnTaxCreditInvestments_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Net loss on tax credit investments</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_MortgageBackedSecuritiesMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Mortgage-Backed Securities [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_MortgageBackedSecuritiesMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Collateralized Mortgage-Backed Securities [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_CorporateNonSegmentMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Segment Reporting, Reconciling Item, Corporate Nonsegment [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_CorporateNonSegmentMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Reconciliation [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_StandbyLettersOfCreditMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Standby Letters Of Credit [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_StandbyLettersOfCreditMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Standby Letters of Credit [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ProceedsFromMaturitiesPrepaymentsAndCallsOfHeldToMaturitySecurities_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Proceeds from Maturities, Prepayments and Calls of Held-to-Maturity Securities</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ProceedsFromMaturitiesPrepaymentsAndCallsOfHeldToMaturitySecurities_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Proceeds from principal payments, maturities and calls on held to maturity securities</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FiniteLivedIntangibleAssetsNet_lbl" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Other intangible assets, net</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FiniteLivedIntangibleAssetsNet_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Finite-Lived Intangible Assets, Net</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FiniteLivedIntangibleAssetsNet_lbl" xlink:role="http://www.xbrl.org/2003/role/periodStartLabel">Finite-Lived Intangible Assets, Net, Beginning Balance</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FiniteLivedIntangibleAssetsNet_lbl" xlink:role="http://www.xbrl.org/2003/role/periodEndLabel">Finite-Lived Intangible Assets, Net, Ending Balance</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FiniteLivedIntangibleAssetsNet_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FiniteLivedIntangibleAssetsNet_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Intangible assets, net - Courier Capital</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_OtherFeesAndIncome_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Other fees and income</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_OtherFeesAndIncome_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Other Fees And Income</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_OtherFeesAndIncome_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Other fees and income.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ScheduleOfInvestmentsTable_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Schedule Of Investments [Table]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ScheduleOfInvestmentsTable_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Schedule of Investments [Table]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_NewAccountingPronouncementsPolicyPolicyTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Recent Accounting Pronouncements</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_NewAccountingPronouncementsPolicyPolicyTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">New Accounting Pronouncements, Policy [Policy Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_LesseeOperatingLeaseLiabilityMaturityTableTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Lessee, Operating Lease, Liability, to be Paid, Maturity [Table Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_LesseeOperatingLeaseLiabilityMaturityTableTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Summary of Future Minimum Payments Under Non-cancellable Operating Leases</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipByIncomeStatementLocationByDerivativeInstrumentRiskTable_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Derivative Instruments Gain Loss By Hedging Relationship By Income Statement Location By Derivative Instrument Risk [Table]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipByIncomeStatementLocationByDerivativeInstrumentRiskTable_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Derivative Instruments, Gain (Loss) [Table]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ScheduleOfComprehensiveIncomeLossTableTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Comprehensive Income (Loss) [Table Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ScheduleOfComprehensiveIncomeLossTableTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Components of Other Comprehensive (Loss) Income</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ComprehensiveIncomeNoteTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Accumulated Other Comprehensive Loss</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ComprehensiveIncomeNoteTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Comprehensive Income (Loss) Note [Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_CarryingReportedAmountFairValueDisclosureMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Carrying Amount [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_CarryingReportedAmountFairValueDisclosureMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Reported Value Measurement [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_InvestmentTypeExtensibleEnumeration_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Investment, Type [Extensible Enumeration]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_AddedWeightedAverageLoansLife_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Added weighted average loans life.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_AddedWeightedAverageLoansLife_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Added Weighted Average Loans Life</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_AddedWeightedAverageLoansLife_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Added Weighted Average Loans Life</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_MortgageBackedSecuritiesDomain_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Mortgage Backed Securities [Domain]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_MortgageBackedSecuritiesDomain_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Mortgage Backed Securities</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansAdjustmentNetOfTax_lbl" xlink:role="http://www.xbrl.org/2009/role/negatedLabel">Pension and post-retirement obligations</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansAdjustmentNetOfTax_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Other Comprehensive (Income) Loss, Defined Benefit Plan, after Reclassification Adjustment, after Tax</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansAdjustmentNetOfTax_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Other Comprehensive (Income) Loss, Defined Benefit Plan, after Reclassification Adjustment, after Tax, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_HeldtomaturitySecuritiesMember_lbl" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Held To Maturity Investment Securities [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_HeldtomaturitySecuritiesMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Held To Maturity Investment Securities [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_HeldtomaturitySecuritiesMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Held-to-Maturity Securities [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_FinancingReceivableAfterDeferredIncomeOffsetAmount_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_FinancingReceivableAfterDeferredIncomeOffsetAmount_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Financing Receivable After Deferred Income Offset Amount</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_FinancingReceivableAfterDeferredIncomeOffsetAmount_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Financing receivable after deferred income offset amount.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_CommonStockSharesOutstanding_lbl" xlink:role="http://www.xbrl.org/2003/role/periodStartLabel">Shares outstanding, beginning balance</link:label>
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          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DefinedBenefitPlanAmortizationOfPriorServiceCostCredit_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Amortization of unrecognized prior service credit</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DefinedBenefitPlanAmortizationOfPriorServiceCostCredit_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Defined Benefit Plan, Amortization of Prior Service Cost (Credit)</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_DocumentTransitionReport_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Document Transition Report</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_DocumentTransitionReport_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Document Transition Report</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DeferredTaxAssetsLiabilitiesNet_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Deferred Tax Assets, Net, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DeferredTaxAssetsLiabilitiesNet_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Deferred Tax Assets, Net</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DeferredTaxAssetsLiabilitiesNet_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Net deferred tax asset</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_HeldToMaturitySecuritiesFairValue_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Securities held to maturity, Fair Value</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_HeldToMaturitySecuritiesFairValue_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Securities held to maturity, fair value</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_HeldToMaturitySecuritiesFairValue_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Debt Securities, Held-to-Maturity, Fair Value</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_LesseeOperatingLeasesTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Leases</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_LesseeOperatingLeasesTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Lessee, Operating Leases [Text Block]</link:label>
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          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ValuationTechniqueDiscountedCashFlowMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Valuation Technique, Discounted Cash Flow [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PaymentsForRepurchaseOfCommonStock_lbl" xlink:role="http://www.xbrl.org/2009/role/negatedLabel">Purchases of common stock for treasury</link:label>
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          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_StatementOfCashFlowsAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Statement of Cash Flows [Abstract]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_WeightedAverageNumberDilutedSharesOutstandingAdjustmentAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Incremental shares from assumed:</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_WeightedAverageNumberDilutedSharesOutstandingAdjustmentAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Weighted Average Number of Shares Outstanding, Diluted, Adjustment [Abstract]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ScheduleOfInterestRateDerivativesTableTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Schedule of Interest Rate Derivatives [Table Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ScheduleOfInterestRateDerivativesTableTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Summary of Company's Outstanding Interest Rate Swaps</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_BrokerageCommissionsRevenue_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Investment advisory</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_BrokerageCommissionsRevenue_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Brokerage Commissions Revenue</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_BrokerageCommissionsRevenue_lbl" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Investment advisory income</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_InterestRateSwapMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Interest Rate Swap [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_InterestRateSwapMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Interest Rate Swap [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_StockholdersEquityNoteDisclosureTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Shareholders' Equity</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_StockholdersEquityNoteDisclosureTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Equity [Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ScheduleOfAccountsNotesLoansAndFinancingReceivableTable_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Schedule Of Accounts Notes Loans And Financing Receivable [Table]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ScheduleOfAccountsNotesLoansAndFinancingReceivableTable_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Accounts and Financing Receivables [Table]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_InvestmentSecuritiesContinuousUnrealizedLossPositionFairValue_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Investment Securities Continuous Unrealized Loss Position Fair Value</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_InvestmentSecuritiesContinuousUnrealizedLossPositionFairValue_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">This item represents the fair value of securities which are in an unrealized loss position.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_InvestmentSecuritiesContinuousUnrealizedLossPositionFairValue_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Total AFS debt securities with unrealized losses, Fair Value</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FiniteLivedIntangibleAssetsLineItems_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Finite-Lived Intangible Assets [Line Items]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_EarningsPerShareTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Earnings Per Common Share ("EPS")</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_EarningsPerShareTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Earnings Per Share [Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Assets measured at fair value on recurring basis using significant unobservable inputs</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue_lbl" xlink:role="http://www.xbrl.org/2003/role/periodStartLabel">Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value, Beginning Balance</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue_lbl" xlink:role="http://www.xbrl.org/2003/role/periodEndLabel">Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value, Ending Balance</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_NetIncomeLoss_lbl" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Net (loss) income</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_NetIncomeLoss_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Net income</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_NetIncomeLoss_lbl" xlink:role="http://www.xbrl.org/2009/role/netLabel">Net income</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_NetIncomeLoss_lbl" xlink:role="http://www.xbrl.org/2009/role/negatedTotalLabel">Net income</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_NetIncomeLoss_lbl" xlink:role="http://www.xbrl.org/2009/role/negatedLabel">Net income</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OtherIntangibleAssetsNet_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Other Intangible Assets, Net</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OtherIntangibleAssetsNet_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Other intangible assets, net</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DebtAndEquitySecuritiesGainLoss_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Debt and Equity Securities, Gain (Loss)</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DebtAndEquitySecuritiesGainLoss_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Debt and Equity Securities, Gain (Loss), Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DebtAndEquitySecuritiesGainLoss_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Net (loss) gain on investment securities</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DebtAndEquitySecuritiesGainLoss_lbl" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Net gain on sale of investment securities</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DebtAndEquitySecuritiesGainLoss_lbl" xlink:role="http://www.xbrl.org/2009/role/negatedLabel">Net gain on investment securities</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DividendsPreferredStockCash_lbl" xlink:role="http://www.xbrl.org/2009/role/negatedLabel">Preferred stock dividends per share</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DividendsPreferredStockCash_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Dividends, Preferred Stock, Cash</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OperatingLeaseCost_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Operating lease costs</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OperatingLeaseCost_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Operating Lease, Cost</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_OperatingLeaseRightOfUseAssetGross_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Gross carrying amount</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_OperatingLeaseRightOfUseAssetGross_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Operating Lease Right Of Use Asset Gross</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_OperatingLeaseRightOfUseAssetGross_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Operating lease right of use asset gross.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OperatingLeasePayments_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Operating cash flows from operating leases</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OperatingLeasePayments_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Operating Lease, Payments</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ProvisionForLoanLeaseAndOtherLosses_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Provision for Loan, Lease, and Other Losses, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ProvisionForLoanLeaseAndOtherLosses_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Provision for Loan, Lease, and Other Losses</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ProvisionForLoanLeaseAndOtherLosses_lbl" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">(Provision) benefit for credit losses</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ProvisionForLoanLeaseAndOtherLosses_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Provision for credit losses</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DerivativesFairValueLineItems_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Derivatives, Fair Value [Line Items]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DerivativesFairValueLineItems_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Derivatives, Fair Value [Line Items]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_LoansMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Loans [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_LoansMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Loans [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AssetsAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">ASSETS</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AssetsAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Assets [Abstract]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_DocumentFiscalYearFocus_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Document Fiscal Year Focus</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_DocumentFiscalYearFocus_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Document Fiscal Year Focus</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_StockReleasedDuringPeriodValueRestrictedStockUnits_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Restricted stock units released</link:label>
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          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_StockReleasedDuringPeriodValueRestrictedStockUnits_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Stock released during period value restricted stock units.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PaymentsForOriginationAndPurchasesOfLoansHeldForSale_lbl" xlink:role="http://www.xbrl.org/2009/role/negatedLabel">Originations of loans held for sale</link:label>
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          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PaymentsForOriginationAndPurchasesOfLoansHeldForSale_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Payments for Origination and Purchases of Loans Held-for-sale, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_TroubledDebtRestructuringsOnFinancingReceivablesTableTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Financing Receivable, Modified [Table Text Block]</link:label>
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          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OtherAssetsMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Other Assets [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OtherAssetsMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Other Assets [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_OperatingLeaseLiabilitiesAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Operating Lease Liabilities:</link:label>
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          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_OperatingLeaseLiabilitiesAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Operating lease liabilities.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Cash flows from investing activities:</link:label>
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          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_InvestmentsInDebtAndMarketableEquitySecuritiesAndCertainTradingAssetsDisclosureTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Investments in Debt and Marketable Equity Securities (and Certain Trading Assets) Disclosure [Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ScheduleOfNetBenefitCostsTableTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Components of Net Periodic Benefit Expense</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ScheduleOfNetBenefitCostsTableTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Schedule of Net Benefit Costs [Table Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ScheduleOfFairValueOffBalanceSheetRisksTable_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Schedule Of Fair Value Off Balance Sheet Risks [Table]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ScheduleOfFairValueOffBalanceSheetRisksTable_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Fair Value, off-Balance-Sheet Risk [Table]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DerivativeMaturityDates_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Derivative, Contract End Date</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DerivativeMaturityDates_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Derivative, Contract End Date</link:label>
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          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AccumulatedDefinedBenefitPlansAdjustmentNetPriorServiceCostCreditMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Prior Service Credit [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AccumulatedDefinedBenefitPlansAdjustmentNetPriorServiceCostCreditMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Accumulated Defined Benefit Plans Adjustment, Net Prior Service Attributable to Parent [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseNextTwelveMonths_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Finite-Lived Intangible Asset, Expected Amortization, Year One</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseNextTwelveMonths_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">2027</link:label>
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          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_ValuationTechniqueAppraisalOfCollateralMember_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Valuation technique appraisal of collateral.</link:label>
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          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ScheduleOfUnrealizedLossOnInvestmentsTableTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Schedule of Unrealized Loss on Investments [Table Text Block]</link:label>
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          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OtherLiabilities_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Other Liabilities</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OtherLiabilities_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Total other liabilities</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PrivateEquityFundsMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Private Equity Funds [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PrivateEquityFundsMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Privately issued</link:label>
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          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_CommitmentsAndContingenciesDisclosureAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Commitments and Contingencies Disclosure [Abstract]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OtherDebtSecuritiesMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Other Debt Obligations [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OtherDebtSecuritiesMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Other Debt Securities [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_InvestmentSecuritiesInUnrealizedLossPositionNumberOfPositions_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Number of security positions, unrealized loss position</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_InvestmentSecuritiesInUnrealizedLossPositionNumberOfPositions_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Investment Securities In Unrealized Loss Position Number Of Positions</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_InvestmentSecuritiesInUnrealizedLossPositionNumberOfPositions_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Number of investments in securities measured at fair value with change in fair value and in unrealized loss position.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTaxAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Net income available to common shareholders</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Net income available to common shareholders</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Net Income (Loss) Available to Common Stockholders, Basic</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DerivativeInstrumentRiskAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Derivative Instrument</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DerivativeInstrumentRiskAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Derivative Instrument [Axis]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DerivativeFinancialInstrumentsAssetsMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Derivative Instruments, Assets [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DerivativeFinancialInstrumentsAssetsMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Derivative Financial Instruments, Assets [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DefinedBenefitPlanInterestCost_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Interest cost on projected benefit obligation</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DefinedBenefitPlanInterestCost_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Defined Benefit Plan, Interest Cost</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Share-Based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Amount</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Unrecognized compensation expense</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Amount, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AssetsFairValueDisclosure_lbl" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Assets at fair value</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AssetsFairValueDisclosure_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Assets at fair value</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AssetsFairValueDisclosure_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Assets, Fair Value Disclosure</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AssetsFairValueDisclosure_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Assets, Fair Value Disclosure, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_SubsidiarySaleOfStockAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Sale of Stock [Axis]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ScheduleOfOtherAssetsAndOtherLiabilitiesTableTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Schedule of Other Assets and Other Liabilities [Table Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ScheduleOfOtherAssetsAndOtherLiabilitiesTableTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Summary of Other Assets and Other Liabilities</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_NetCashProvidedByUsedInInvestingActivities_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Cash Provided by (Used in) Investing Activity, Including Discontinued Operation</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_NetCashProvidedByUsedInInvestingActivities_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Net cash used in investing activities</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PassMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Uncriticized [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PassMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Pass [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_Security12bTitle_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Title of 12(b) Security</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_Security12bTitle_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Title of 12(b) Security</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Schedule Of Segment Reporting Information By Segment [Table]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Schedule of Segment Reporting Information, by Segment [Table]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosureTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Derivative Instruments and Hedging Activities Disclosure [Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosureTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Derivative Instruments and Hedging Activities</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_LoansAndLeasesReceivableDisclosureAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Loans and Leases Receivable Disclosure [Abstract]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterOneThroughFiveYearsAmortizedCost_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Debt Securities, Available-for-Sale, Amortized Cost, Maturity, Allocated and Single Maturity Date, after Year One Through Five</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterOneThroughFiveYearsAmortizedCost_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Debt securities available for sale, Due after one to five years, Amortized Cost</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DebtSecuritiesAvailableForSaleAllowanceForCreditLoss_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Available for sale securities, allowance for credit loss</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DebtSecuritiesAvailableForSaleAllowanceForCreditLoss_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Debt Securities, Available-for-Sale, Allowance for Credit Loss</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DebtSecuritiesAvailableForSaleAllowanceForCreditLoss_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Debt Securities, Available-for-sale, Allowance for Credit Loss, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DebtSecuritiesAvailableForSaleAllowanceForCreditLoss_lbl" xlink:role="http://www.xbrl.org/2003/role/periodStartLabel">Debt Securities, Available-for-sale, Allowance for Credit Loss, Beginning Balance</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DebtSecuritiesAvailableForSaleAllowanceForCreditLoss_lbl" xlink:role="http://www.xbrl.org/2003/role/periodEndLabel">Debt Securities, Available-for-sale, Allowance for Credit Loss, Ending Balance</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_InvestmentSecuritiesContinuousUnrealizedLossPositionLessThanTwelveMonthsFairValue_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Total AFS debt securities with unrealized losses, Less than 12 months, Fair Value</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_InvestmentSecuritiesContinuousUnrealizedLossPositionLessThanTwelveMonthsFairValue_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Investment Securities Continuous Unrealized Loss Position Less Than Twelve Months Fair Value</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_InvestmentSecuritiesContinuousUnrealizedLossPositionLessThanTwelveMonthsFairValue_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">This item represents the fair value of securities that have been in a continuous unrealized loss position for less than twelve months.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_InvestmentSecuritiesContinuousUnrealizedLossPositionLessThanTwelveMonthsFairValue_lbl" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Securities, Less than 12 months, Fair Value</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_ShareholdersEquityTable_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Shareholders Equity [Table]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_ShareholdersEquityTable_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Shareholders Equity [Table]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_ShareholdersEquityTable_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Shareholders Equity [Table]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_WeightedAverageNumberOfSharesIssuedBasic_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Total shares issued</link:label>
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          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_InterestExpenseShortTermBorrowings_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Short-term borrowings</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_InterestExpenseShortTermBorrowings_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Interest Expense, Short-Term Borrowings</link:label>
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          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterOneThroughFiveYearsFairValue_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Debt securities available for sale, Due from one to five years, Fair Value</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterOneThroughFiveYearsFairValue_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Debt Securities, Available-for-Sale, Fair Value, Maturity, Allocated and Single Maturity Date, after Year One Through Five</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DividendsCashAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Cash dividends declared:</link:label>
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          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_HeldToMaturitySecuritiesDebtMaturitiesAfterOneThroughFiveYearsFairValue_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Debt securities held to maturity, Due from one to five years, Fair Value</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_HeldToMaturitySecuritiesDebtMaturitiesAfterOneThroughFiveYearsFairValue_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Debt Securities, Held-to-Maturity, Fair Value, Maturity, Allocated and Single Maturity Date, after Year One Through Five</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_TimeDeposits_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Time deposits</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_TimeDeposits_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Time Deposits</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_TimeDeposits_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Time Deposits, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Table]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Fair Value, Recurring and Nonrecurring [Table]</link:label>
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          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AdditionalPaidInCapitalMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Additional Paid-in Capital [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AdditionalPaidInCapitalMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Additional Paid-in Capital [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_HeldToMaturitySecuritiesDebtMaturitiesAfterFiveThroughTenYearsFairValue_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Debt securities held to maturity, Due after five years through ten years, Fair Value</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_HeldToMaturitySecuritiesDebtMaturitiesAfterFiveThroughTenYearsFairValue_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Debt Securities, Held-to-Maturity, Fair Value, Maturity, Allocated and Single Maturity Date, after Year 5 Through 10</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FairValueMeasurementFrequencyDomain_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Measurement Frequency</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FairValueMeasurementFrequencyDomain_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Measurement Frequency [Domain]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_IncomeStatementLocationAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Income Statement Location</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_IncomeStatementLocationAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Statement of Income Location, Balance [Axis]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ReclassificationAdjustmentOutOfAccumulatedOtherComprehensiveIncomeLineItems_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ReclassificationAdjustmentOutOfAccumulatedOtherComprehensiveIncomeLineItems_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_TradingSymbol_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Trading Symbol</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_TradingSymbol_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Trading Symbol</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Intangible Asset, Finite-Lived [Table]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Schedule Of Finite Lived Intangible Assets [Table]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AvailableForSaleSecuritiesDebtMaturitiesWithinOneYearAmortizedCost_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Debt securities available for sale, Due in one year or less, Amortized Cost</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AvailableForSaleSecuritiesDebtMaturitiesWithinOneYearAmortizedCost_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Debt Securities, Available-for-Sale, Amortized Cost, Maturity, Allocated and Single Maturity Date, Year One</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTableTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Gross Carrying Amount Accumulated Amortization and Net Book Value</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTableTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Schedule of Finite-Lived Intangible Assets [Table Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AllowanceForCreditLossesOnFinancingReceivablesTableTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Changes in the Allowance for Loan Losses</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AllowanceForCreditLossesOnFinancingReceivablesTableTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Financing Receivable, Allowance for Credit Loss [Table Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Cash flows from financing activities:</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Cash Provided by (Used in) Financing Activity, Including Discontinued Operation [Abstract]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_CollateralizedMortgageObligationsMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Collateralized Mortgage Obligations [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_CollateralizedMortgageObligationsMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Collateralized Mortgage Obligations [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FairValueMeasurementsRecurringMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Measured On A Recurring Basis [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FairValueMeasurementsRecurringMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Fair Value, Recurring [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ScheduleOfImpairedFinancingReceivableTable_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Schedule Of Impaired Financing Receivable [Table]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ScheduleOfImpairedFinancingReceivableTable_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Schedule of Impaired Financing Receivable [Table]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_LesseeOperatingLeaseLiabilityPaymentsDue_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Total future minimum operating lease payments</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_LesseeOperatingLeaseLiabilityPaymentsDue_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Lessee, Operating Lease, Liability, to be Paid</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_CollateralizedMortgageBackedSecuritiesGovernmentNationalMortgageAssociationCertificatesAndObligationsGnmaMember_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Collateralized Mortgage-Backed Securities Government National Mortgage Association Certificates and Obligations (GNMA).</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_CollateralizedMortgageBackedSecuritiesGovernmentNationalMortgageAssociationCertificatesAndObligationsGnmaMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Collateralized Mortgage-Backed Securities Government National Mortgage Association Certificates and Obligations (GNMA) [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AccountingStandardsUpdate201613Member_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">ASU 2016-13 [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AccountingStandardsUpdate201613Member_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Accounting Standards Update 2016-13 [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_LesseeOperatingLeaseLiabilityUndiscountedExcessAmount_lbl" xlink:role="http://www.xbrl.org/2009/role/negatedLabel">Amounts representing interest</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_LesseeOperatingLeaseLiabilityUndiscountedExcessAmount_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Lessee, Operating Lease, Liability, Undiscounted Excess Amount</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Fair Value Inputs, Assets, Quantitative Information [Line Items]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Fair Value Measurement Inputs and Valuation Techniques [Line Items]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FinancingReceivablePortfolioSegmentDomain_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Financing Receivable Portfolio Segment [Domain]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AccumulatedNetInvestmentGainLossIncludingPortionAttributableToNoncontrollingInterestMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Securities Available for Sale and Transferred Securities [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AccumulatedNetInvestmentGainLossIncludingPortionAttributableToNoncontrollingInterestMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">AOCI, Accumulated Gain (Loss), Debt Securities, Available-for-Sale, Including Noncontrolling Interest [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OtherThanTemporaryImpairmentCreditLossesRecognizedInEarningsCategoriesOfInvestmentsDomain_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Other than Temporary Impairment, Credit Losses Recognized in Earnings, Categories of Investments</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OtherThanTemporaryImpairmentCreditLossesRecognizedInEarningsCategoriesOfInvestmentsDomain_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Other than Temporary Impairment, Credit Losses Recognized in Earnings, Categories of Investments [Domain]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_InterestAndDividendIncomeSecurities_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Interest and dividends on investment securities</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_InterestAndDividendIncomeSecurities_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Interest and Dividend Income, Securities, Operating</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_InterestAndDividendIncomeSecurities_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Total interest and dividends on securities</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_StatementEquityComponentsAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Equity Components</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_StatementEquityComponentsAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Equity Components [Axis]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FinancingReceivableRevolving_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Revolving Loans Amortized Cost Basis</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FinancingReceivableRevolving_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Financing Receivable, Revolving</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_EquityComponentDomain_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Equity Component</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_EquityComponentDomain_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Equity Component [Domain]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FairValueByAssetClassAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Asset Class</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FairValueByAssetClassAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Asset Class [Axis]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_GoodwillAndIntangibleAssetsDisclosureAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Goodwill and Intangible Assets Disclosure [Abstract]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_CardInterchangeIncome_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Card interchange income.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_CardInterchangeIncome_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Card interchange income</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_CardInterchangeIncome_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Card Interchange Income</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OtherNoninterestExpense_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Other</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OtherNoninterestExpense_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Other Noninterest Expense</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OtherNoninterestExpense_lbl" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Other noninterest expense</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_CommercialCollateralizedMortgageMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Commercial Collateralized Mortgage [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_CommercialCollateralizedMortgageMember_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Commercial collateralized mortgage.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_BankOwnedLifeInsurance_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Bank Owned Life Insurance</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_BankOwnedLifeInsurance_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Company owned life insurance</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OperatingLeaseLiabilityStatementOfFinancialPositionExtensibleList_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Operating Lease, Liability, Statement of Financial Position [Extensible List]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OperatingLeaseLiabilityStatementOfFinancialPositionExtensibleList_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Operating Lease, Liability, Statement of Financial Position [Extensible Enumeration]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterFiveThroughTenYearsAmortizedCost_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Debt securities available for sale, Due after five years through ten years, Amortized Cost</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterFiveThroughTenYearsAmortizedCost_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Debt Securities, Available-for-Sale, Amortized Cost, Maturity, Allocated and Single Maturity Date, after Year 5 Through 10</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DepreciationAndAmortization_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Depreciation and amortization</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DepreciationAndAmortization_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Depreciation, Depletion and Amortization, Nonproduction</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DepreciationAndAmortization_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Depreciation, Depletion and Amortization, Nonproduction, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_NotesReceivableNet_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Total loans, net</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_NotesReceivableNet_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Financing receivables, amortized cost basis</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_NotesReceivableNet_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Loans (net of allowance for credit losses of $47,291 and $48,041, respectively)</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_NotesReceivableNet_lbl" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Loans (net of allowance for credit losses of $47,497 and $47,386, respectively)</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_StatementOfIncomeAndComprehensiveIncomeAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Statement of Comprehensive Income [Abstract]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OtherAssetsAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Other Assets [Abstract]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_DebtSecuritiesAvailableForSaleAndHeldToMaturitySecuritiesTable_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Debt Securities Available For Sale And Held To Maturity Securities [Table]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_DebtSecuritiesAvailableForSaleAndHeldToMaturitySecuritiesTable_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Debt Securities Available For Sale And Held To Maturity Securities [Table]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_DebtSecuritiesAvailableForSaleAndHeldToMaturitySecuritiesTable_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Debt securities available for sale and held to maturity securities.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="srt_MaximumMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Maximum [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="srt_MaximumMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Maximum [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_LiabilitiesFairValueDisclosure_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Liabilities at fair value</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_LiabilitiesFairValueDisclosure_lbl" xlink:role="http://www.xbrl.org/2009/role/negatedLabel">Liabilities at fair value</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_LiabilitiesFairValueDisclosure_lbl" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Liabilities measured at fair value on nonrecurring basis</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_LiabilitiesFairValueDisclosure_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Liabilities, Fair Value Disclosure</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_LiabilitiesFairValueDisclosure_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Liabilities, Fair Value Disclosure, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DesignatedAsHedgingInstrumentMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Derivatives Designated as Hedging Instruments [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DesignatedAsHedgingInstrumentMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Designated as Hedging Instrument [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ScheduleOfStockByClassTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Changes in Shares of Common Stock</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ScheduleOfStockByClassTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Schedule of Stock by Class [Table Text Block]</link:label>
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          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DerivativeFixedInterestRate_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Derivative fixed strike price</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DerivativeFixedInterestRate_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Derivative, Fixed Interest Rate</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ScheduleOfFinancingReceivableAllowanceForCreditLossesTable_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Schedule Of Financing Receivable Allowance For Credit Losses [Table]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ScheduleOfFinancingReceivableAllowanceForCreditLossesTable_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Financing Receivable, Allowance for Credit Loss [Table]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeTableTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Reclassification out of Accumulated Other Comprehensive Income [Table Text Block]</link:label>
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          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DebtSecuritiesAvailableForSaleRealizedGain_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Debt Securities, Available-for-Sale, Realized Gain</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DebtSecuritiesAvailableForSaleRealizedGain_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Gross realized gains</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ComprehensiveIncomeNetOfTaxAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Comprehensive income (loss):</link:label>
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          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PreferredStockDividendsIncomeStatementImpact_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Preferred stock dividends</link:label>
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          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_BankOwnedLifeInsuranceIncome_lbl" xlink:role="http://www.xbrl.org/2009/role/negatedLabel">Income on company owned life insurance</link:label>
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          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_OperatingLeaseRightOfUseAssetsAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Operating Lease Right of Use Assets:</link:label>
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          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_OperatingLeaseRightOfUseAssetsAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Operating lease right of use assets.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ScheduleofFiniteLivedIntangibleAssetsFutureAmortizationExpenseTableTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Estimated Amortization Expense of Other Intangible Assets</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ScheduleofFiniteLivedIntangibleAssetsFutureAmortizationExpenseTableTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Schedule of Finite-Lived Intangible Assets, Future Amortization Expense [Table Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_InvestmentSecuritiesContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Investment Securities Continuous Unrealized Loss Position12 Months Or Longer Accumulated Loss</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_InvestmentSecuritiesContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Amount of accumulated pre-tax unrealized loss on securities that have been in a loss position for twelve months or longer.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_InvestmentSecuritiesContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss_lbl" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Securities, 12 months or longer, Unrealized Losses</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_InvestmentSecuritiesContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Total AFS debt securities with unrealized losses, 12 months or longer, Unrealized Losses</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FairValueOffBalanceSheetRisksDisclosureInformationLineItems_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FairValueOffBalanceSheetRisksDisclosureInformationLineItems_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Fair Value, off-Balance-Sheet Risks, Disclosure Information [Line Items]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PreferredStockSharesAuthorized_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Preferred stock, shares authorized</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PreferredStockSharesAuthorized_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Preferred Stock, Shares Authorized</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_InterestPayableCurrent_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Accrued interest payable</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_InterestPayableCurrent_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Interest Payable, Current</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Finite-Lived Intangible Assets by Major Class [Axis]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Finite-Lived Intangible Assets by Major Class</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_HeldToMaturitySecuritiesDebtMaturitiesAfterTenYearsFairValue_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Debt securities held to maturity, Due after ten years, Fair Value</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_HeldToMaturitySecuritiesDebtMaturitiesAfterTenYearsFairValue_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Debt Securities, Held-to-Maturity, Fair Value, Maturity, Allocated and Single Maturity Date, after Year 10</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DebtSecuritiesAvailableForSaleUnrealizedLossPositionAccumulatedLoss_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Securities available for sale, Unrealized Losses, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DebtSecuritiesAvailableForSaleUnrealizedLossPositionAccumulatedLoss_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Debt Securities, Available-for-Sale, Unrealized Loss Position, Accumulated Loss</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FederalNationalMortgageAssociationCertificatesAndObligationsFNMAMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Federal National Mortgage Association [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FederalNationalMortgageAssociationCertificatesAndObligationsFNMAMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Federal National Mortgage Association Certificates and Obligations (FNMA) [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FairValueBalanceSheetGroupingFinancialStatementCaptionsLineItems_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FairValueBalanceSheetGroupingFinancialStatementCaptionsLineItems_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_InformationByCategoryOfDebtSecurityAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Debt Security Category</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_InformationByCategoryOfDebtSecurityAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Debt Security Category [Axis]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_InterestBearingDepositLiabilities_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Interest-bearing demand</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_InterestBearingDepositLiabilities_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Interest-Bearing Deposit Liabilities</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_InterestBearingDepositLiabilities_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Interest-bearing Deposit Liabilities, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DerivativeFinancialInstrumentsLiabilitiesMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Derivative Instruments, Liabilities [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DerivativeFinancialInstrumentsLiabilitiesMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Derivative Financial Instruments, Liabilities [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AccountsNotesAndLoansReceivableLineItems_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Accounts, Notes, Loans and Financing Receivable [Line Items]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AccountsNotesAndLoansReceivableLineItems_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Accounts, Notes, Loans and Financing Receivable [Line Items]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_EntityRegistrantName_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Entity Registrant Name</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_EntityRegistrantName_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Entity Registrant Name</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Securities available for sale, Unrealized Losses</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Debt Securities, Available-for-Sale, Accumulated Gross Unrealized Loss, before Tax</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearTwo_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Finite-Lived Intangible Asset, Expected Amortization, Year Two</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearTwo_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">2028</link:label>
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          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_TreasuryStockSharesAcquired_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Treasury Stock, Shares, Acquired</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_TreasuryStockSharesAcquired_lbl" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Treasury stock purchases</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AdditionalPaidInCapital_lbl" xlink:role="http://www.xbrl.org/2003/role/periodEndLabel">Additional Paid in Capital, Ending Balance</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AdditionalPaidInCapital_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Additional paid-in capital</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AdditionalPaidInCapital_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Additional Paid in Capital</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AdditionalPaidInCapital_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Additional Paid in Capital, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AdditionalPaidInCapital_lbl" xlink:role="http://www.xbrl.org/2003/role/periodStartLabel">Additional Paid in Capital, Beginning Balance</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AccumulatedOtherComprehensiveIncomeLossTable_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Accumulated Other Comprehensive Income Loss [Table]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AccumulatedOtherComprehensiveIncomeLossTable_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Accumulated Other Comprehensive Income (Loss) [Table]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearThree_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Finite-Lived Intangible Asset, Expected Amortization, Year Three</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearThree_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">2029</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_IncomeTaxExpenseBenefit_lbl" xlink:role="http://www.xbrl.org/2009/role/negatedTerseLabel">Income tax (expense) benefit</link:label>
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          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_IncomeTaxExpenseBenefit_lbl" xlink:role="http://www.xbrl.org/2009/role/negatedLabel">Income tax benefit (expense)</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FairValueByMeasurementFrequencyAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Measurement Frequency</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FairValueByMeasurementFrequencyAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Measurement Frequency [Axis]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_DebtSecuritiesAvailableForSaleAndHeldToMaturitySecuritiesLineItems_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Schedule of Debt Securities Available For Sale and Held To Maturity Securities [Line Item]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_DebtSecuritiesAvailableForSaleAndHeldToMaturitySecuritiesLineItems_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Debt Securities Available For Sale And Held To Maturity Securities [Line Items]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_DebtSecuritiesAvailableForSaleAndHeldToMaturitySecuritiesLineItems_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Debt securities available for sale and held to maturity securities.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FederalHomeLoanMortgageCorporationCertificatesAndObligationsFHLMCMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Federal Home Loan Mortgage Corporation [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FederalHomeLoanMortgageCorporationCertificatesAndObligationsFHLMCMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Federal Home Loan Mortgage Corporation Certificates and Obligations (FHLMC) [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Share-based Compensation Arrangement by Share-based Payment Award [Line Items]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]</link:label>
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          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTableTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Fair Value Measurement Inputs and Valuation Techniques [Table Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ProceedsFromLifeInsurancePolicies_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Proceeds from Life Insurance Policy</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ProceedsFromLifeInsurancePolicies_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Proceeds received from surrender of company owned life insurance</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_CommercialLoanMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Commercial Loan [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_EntityCommonStockSharesOutstanding_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Entity Common Stock, Shares Outstanding</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_EntityCommonStockSharesOutstanding_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Entity Common Stock, Shares Outstanding</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_USStatesAndPoliticalSubdivisionsMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">State And Political Subdivisions [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_USStatesAndPoliticalSubdivisionsMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">US States and Political Subdivisions Debt Securities [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FairValueByLiabilityClassAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Liability Class</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FairValueByLiabilityClassAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Liability Class [Axis]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Accumulated Other Comprehensive Income (Loss), Net of Tax</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Accumulated Other Comprehensive Income (Loss), Net of Tax, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Accumulated other comprehensive loss</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="srt_ConsolidationItemsAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Consolidation Items</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="srt_ConsolidationItemsAxis_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Consolidation Items [Axis]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_HeldToMaturitySecuritiesNet_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Held-to-maturity securities, net , Amortized Cost</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_HeldToMaturitySecuritiesNet_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Held-to-maturity securities, net , Amortized Cost</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_HeldToMaturitySecuritiesNet_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Held To Maturity Securities Net</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_HeldToMaturitySecuritiesNet_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Held-to-maturity securities, net.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_HeldToMaturitySecuritiesNet_lbl" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Securities held to maturity, at amortized cost (net of allowance for credit losses of $2) (fair value of $70,899 and $76,256, respectively)</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PaymentsToAcquirePropertyPlantAndEquipment_lbl" xlink:role="http://www.xbrl.org/2009/role/negatedLabel">Purchases of premises and equipment</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PaymentsToAcquirePropertyPlantAndEquipment_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Payments to Acquire Property, Plant, and Equipment</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PaymentsToAcquirePropertyPlantAndEquipment_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Payments to Acquire Property, Plant, and Equipment, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Granted, Number of Shares</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Grants in Period</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_lbl" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Restricted shares of common stock awarded</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_Assets_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Total assets</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_Assets_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Total assets</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_Assets_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Assets</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_Assets_lbl" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Assets</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PerformingFinancingReceivableMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Performing [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PerformingFinancingReceivableMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Performing Financial Instruments [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Class of Financing Receivable</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Class of Financing Receivable [Domain]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_IncomeStatementAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Income Statement [Abstract]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FinancingReceivableRecordedInvestmentPastDueLineItems_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Financing Receivable, Recorded Investment, Past Due [Line Items]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FinancingReceivableRecordedInvestmentPastDueLineItems_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Financing Receivable, Past Due [Line Items]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DefinedBenefitPlanAmortizationOfGainsLosses_lbl" xlink:role="http://www.xbrl.org/2009/role/negatedLabel">Amortization of unrecognized net actuarial loss</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DefinedBenefitPlanAmortizationOfGainsLosses_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Defined Benefit Plan, Amortization of Gain (Loss)</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DeferredIncomeTaxExpenseBenefit_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Deferred Income Tax Expense (Benefit)</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DeferredIncomeTaxExpenseBenefit_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Deferred Income Tax Expense (Benefit), Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DeferredIncomeTaxExpenseBenefit_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Deferred income tax expense</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="srt_WeightedAverageMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Weighted Average [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="srt_WeightedAverageMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Weighted Average [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_FairValueMeasurementWithUnobservableInputValuePercentage_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Unobservable Input Value or Range</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_FairValueMeasurementWithUnobservableInputValuePercentage_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Fair Value Measurement With Unobservable Input Value Percentage</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_FairValueMeasurementWithUnobservableInputValuePercentage_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Fair value measurement with unobservable input value percentage.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_GainLossOnSalesOfLoansNet_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Gain (Loss) on Sales of Loans, Net</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_GainLossOnSalesOfLoansNet_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Gain (Loss) on Sales of Loans, Net, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_GainLossOnSalesOfLoansNet_lbl" xlink:role="http://www.xbrl.org/2009/role/negatedLabel">Net gain on sale of loans held for sale</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_GainLossOnSalesOfLoansNet_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Net gain on sale of loans held for sale</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_CommercialAndIndustrialMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Commercial Business [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_CommercialAndIndustrialMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Commercial And Industrial [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_CommercialAndIndustrialMember_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Commercial And Industrial [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_LeaseCostAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Lease, Cost [Abstract]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_LeaseCostAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Lease costs:</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_BusinessCombinationsAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Business Combination [Abstract]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_EarningsPerShareDiluted_lbl" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Diluted earnings per common share</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_EarningsPerShareDiluted_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Diluted</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_EarningsPerShareDiluted_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Earnings Per Share, Diluted</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_EarningsPerShareDiluted_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Earnings Per Share, Diluted, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_ProvisionForCreditLossesMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Provision for Credit Losses [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_ProvisionForCreditLossesMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Provision For Credit Losses [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_ProvisionForCreditLossesMember_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Provision for credit losses.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FinancingReceivableRecordedInvestmentNonaccrualStatus_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Investment securities, nonaccrual</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FinancingReceivableRecordedInvestmentNonaccrualStatus_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Financing Receivable, Nonaccrual</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OperatingSegmentsMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Operating Segment [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OperatingSegmentsMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Operating Segments [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearFive_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Finite-Lived Intangible Asset, Expected Amortization, Year Five</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearFive_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">2031</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_CityAreaCode_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">City Area Code</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_CityAreaCode_lbl" xlink:role="http://www.xbrl.org/2003/role/label">City Area Code</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OtherComprehensiveIncomeLossNetOfTax_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Other Comprehensive Income (Loss), Net of Tax</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OtherComprehensiveIncomeLossNetOfTax_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Other comprehensive income (loss), net of tax</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OtherComprehensiveIncomeLossNetOfTax_lbl" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Net current period other comprehensive (loss) income</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OtherComprehensiveIncomeLossNetOfTax_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Total other comprehensive (loss) income, net of tax</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_Deposits_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Total deposits</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_Deposits_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Deposits</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_DerivativesEffectiveDate_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Derivatives effective date.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_DerivativesEffectiveDate_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Derivatives Effective Date</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_CommercialRealEstateMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Commercial Mortgage [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_CommercialRealEstateMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Commercial Real Estate [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_LoansAndLeasesReceivableDeferredLoanFeesCosts_lbl" xlink:role="http://www.xbrl.org/2009/role/negatedLabel">Net Deferred Loan (Fees) Costs</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_LoansAndLeasesReceivableDeferredLoanFeesCosts_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Loans And Leases Receivable Deferred Loan Fees Costs</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_LoansAndLeasesReceivableDeferredLoanFeesCosts_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Loans and leases receivable deferred loan (fees) costs.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_LoansAndLeasesReceivableDeferredLoanFeesCosts_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Net Deferred Loan (Fees) Costs</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FinancialAssetPastDueMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Financial Asset, Past Due [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FinancialAssetPastDueMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Total Past Due [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OtherIntangibleAssetsMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Other Intangible Assets [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OtherIntangibleAssetsMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Other Intangible Assets [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_InterestAndFeeIncomeLoansAndLeases_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Interest and fees on loans</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_InterestAndFeeIncomeLoansAndLeases_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Interest and Fee Income, Loans and Leases</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_InterestAndFeeIncomeLoansAndLeases_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Interest and Fee Income, Loans and Leases, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FinancingReceivableRevolvingConvertedToTermLoan_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Revolving Loans Converted to Term</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FinancingReceivableRevolvingConvertedToTermLoan_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Financing Receivable, Revolving, Converted to Term Loan</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_VariableLeaseCost_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Variable lease costs</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_VariableLeaseCost_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Variable Lease, Cost</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_LoansHeldForSaleFairValueDisclosure_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Loans held for sale</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_LoansHeldForSaleFairValueDisclosure_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Loan, Held-for-Sale, Fair Value Disclosure</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OtherComprehensiveIncomeLossBeforeTaxPortionAttributableToParent_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Other Comprehensive Income (Loss), before Tax, Portion Attributable to Parent</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OtherComprehensiveIncomeLossBeforeTaxPortionAttributableToParent_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Other comprehensive income (loss), Pre-tax Amount</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OperatingLeaseWeightedAverageRemainingLeaseTerm1_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Operating Lease, Weighted Average Remaining Lease Term</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OperatingLeaseWeightedAverageRemainingLeaseTerm1_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Operating leases, weighted average remaining lease term</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_SegmentReportingInformationLineItems_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Segment Reporting Information [Line Items]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_SegmentReportingInformationLineItems_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Segment Reporting Information [Line Items]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_StockIssuedDuringPeriodSharesRestrictedStockAwardGross_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Restricted stock awards issued</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_StockIssuedDuringPeriodSharesRestrictedStockAwardGross_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Stock Issued During Period, Shares, Restricted Stock Award, Gross</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_LeaseCost_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Lease, Cost</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_LeaseCost_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Net lease costs</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DerivativeFairValueOfDerivativeLiability_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Liability derivatives</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DerivativeFairValueOfDerivativeLiability_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Derivative Liability, Subject to Master Netting Arrangement, before Offset</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DerivativeFairValueOfDerivativeLiability_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Derivative Liability, Fair Value, Gross Liability, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DerivativeFairValueOfDerivativeLiability_lbl" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Derivative instruments</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_InvestmentsAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Investments [Abstract]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_TaxCreditInvestments_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Tax credit investments</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_TaxCreditInvestments_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Tax Credit Investments</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_TaxCreditInvestments_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Tax credit investments.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_TroubledDebtRestructuringsOnFinancingReceivablesModificationEffectTableTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Troubled debt restructurings on financing receivables modification effect.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_TroubledDebtRestructuringsOnFinancingReceivablesModificationEffectTableTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Troubled Debt Restructurings On Financing Receivables Modification Effect [Table Text Block]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_TroubledDebtRestructuringsOnFinancingReceivablesModificationEffectTableTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Financial Effect of the Modifications Made to Borrowers Experiencing Financial Difficulty</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PropertyPlantAndEquipmentNet_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Premises and equipment, net</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PropertyPlantAndEquipmentNet_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Property, Plant and Equipment, Net</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PropertyPlantAndEquipmentNet_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Property, Plant and Equipment, Net, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PropertyPlantAndEquipmentNet_lbl" xlink:role="http://www.xbrl.org/2003/role/periodStartLabel">Property, Plant and Equipment, Net, Beginning Balance</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_PropertyPlantAndEquipmentNet_lbl" xlink:role="http://www.xbrl.org/2003/role/periodEndLabel">Property, Plant and Equipment, Net, Ending Balance</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_StockIssuedDuringPeriodValueRestrictedStockAwardNetOfForfeitures_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Restricted stock awards issued</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_StockIssuedDuringPeriodValueRestrictedStockAwardNetOfForfeitures_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Stock Issued During Period, Value, Restricted Stock Award, Net of Forfeitures</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_StockIssuedDuringPeriodValueRestrictedStockAwardNetOfForfeitures_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Stock Issued During Period, Value, Restricted Stock Award, Net of Forfeitures, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_InvestmentSecuritiesContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Investment Securities Continuous Unrealized Loss Position Less Than12 Months Accumulated Loss</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_InvestmentSecuritiesContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Amount of accumulated pre-tax unrealized loss on investments in securities that have been in a loss position for less than twelve months.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_InvestmentSecuritiesContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss_lbl" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Securities, Less than 12 months, Unrealized Losses</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_InvestmentSecuritiesContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Total AFS debt securities with unrealized losses, Less than 12 months, Unrealized Losses</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsIncludingDisposalGroupAndDiscontinuedOperations_lbl" xlink:role="http://www.xbrl.org/2003/role/periodStartLabel">Cash and cash equivalents, beginning of period</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsIncludingDisposalGroupAndDiscontinuedOperations_lbl" xlink:role="http://www.xbrl.org/2003/role/periodEndLabel">Cash and cash equivalents, end of period</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsIncludingDisposalGroupAndDiscontinuedOperations_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Cash, Cash Equivalent, Restricted Cash, and Restricted Cash Equivalent, Including Discontinued Operation</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsIncludingDisposalGroupAndDiscontinuedOperations_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents, Including Disposal Group and Discontinued Operations, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_RetainedEarningsMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Retained Earnings [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_RetainedEarningsMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Retained Earnings [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AccumulatedDefinedBenefitPlansAdjustmentNetUnamortizedGainLossMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Net Actuarial Losses [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AccumulatedDefinedBenefitPlansAdjustmentNetUnamortizedGainLossMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Accumulated Defined Benefit Plans Adjustment, Net Gain (Loss) Attributable to Parent [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ShareBasedCompensation_lbl" xlink:role="http://www.xbrl.org/2003/role/verboseLabel">Total share-based compensation expense</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ShareBasedCompensation_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Share-based compensation</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ShareBasedCompensation_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Share-Based Payment Arrangement, Noncash Expense</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ShareBasedCompensation_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Share-based Payment Arrangement, Noncash Expense, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_NoninterestIncomeOtherOperatingIncome_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Other</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_NoninterestIncomeOtherOperatingIncome_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Noninterest Income, Other Operating Income</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="srt_StockRepurchaseProgramNumberOfSharesAuthorizedToBeRepurchased_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Shares of common stock authorized to be repurchased</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="srt_StockRepurchaseProgramNumberOfSharesAuthorizedToBeRepurchased_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Share Repurchase Program, Authorized, Number of Shares</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12Months_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Securities available for sale, Less than 12 months, Fair Value</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12Months_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Debt Securities, Available-for-Sale, Continuous Unrealized Loss Position, Less than 12 Months</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OperatingLeaseWeightedAverageDiscountRatePercent_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Operating leases, weighted-average discount rate</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_OperatingLeaseWeightedAverageDiscountRatePercent_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Operating Lease, Weighted Average Discount Rate, Percent</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FairValueInputsLevel1Member_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Level 1 Inputs [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FairValueInputsLevel1Member_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Fair Value, Inputs, Level 1 [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_NetCashProvidedByUsedInFinancingActivities_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Cash Provided by (Used in) Financing Activity, Including Discontinued Operation</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_NetCashProvidedByUsedInFinancingActivities_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Net cash provided by financing activities</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_UnamortizedDebtIssuanceExpense_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Debt issuance costs</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_UnamortizedDebtIssuanceExpense_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Unamortized Debt Issuance Expense</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FinancingReceivableOriginatedThreeYearsBeforeLatestFiscalYear_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Prior Fiscal Year 3</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FinancingReceivableOriginatedThreeYearsBeforeLatestFiscalYear_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Financing Receivable, Year Four, Originated, Three Years before Current Fiscal Year</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterFiveThroughTenYearsFairValue_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Debt securities available for sale, Due after five years through ten years, Fair Value</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterFiveThroughTenYearsFairValue_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Debt Securities, Available-for-Sale, Fair Value, Maturity, Allocated and Single Maturity Date, after Year 5 Through 10</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DerivativeContractTypeDomain_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Derivative Contract</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DerivativeContractTypeDomain_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Derivative Contract [Domain]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_LoanServicingRightsMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Loan Servicing Rights [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_LoanServicingRightsMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Loan Servicing Rights [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_LoanServicingRightsMember_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Loan servicing rights.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FinancingReceivableModificationsLineItems_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Financing Receivable, Modified [Line Items]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_EntityInteractiveDataCurrent_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Entity Interactive Data Current</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="dei_EntityInteractiveDataCurrent_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Entity Interactive Data Current</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_IncomeStatementLocationDomain_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Income Statement Location</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_IncomeStatementLocationDomain_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Statement of Income Location, Balance [Domain]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FairValueDisclosureItemAmountsDomain_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Fair Value Measurement</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_FairValueDisclosureItemAmountsDomain_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Fair Value Measurement [Domain]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_MultifamilyMortgageMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Multifamily [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_MultifamilyMortgageMember_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Multifamily mortgage.</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_MultifamilyMortgageMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Multifamily Mortgage [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Cash flows from operating activities:</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Cash Provided by (Used in) Operating Activity, Including Discontinued Operation [Abstract]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_StockGrantedDuringPeriodValueSharebasedCompensation_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Stock awards</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_StockGrantedDuringPeriodValueSharebasedCompensation_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Shares Granted, Value, Share-Based Payment Arrangement, after Forfeiture</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_StockGrantedDuringPeriodValueSharebasedCompensation_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Shares Granted, Value, Share-based Payment Arrangement, after Forfeiture, Total</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_LoanRestructuringModificationDomain_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Loan Restructuring Modification</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_LoanRestructuringModificationDomain_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Loan Restructuring Modification [Domain]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AccretionAmortizationOfDiscountsAndPremiumsInvestments_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Accretion (Amortization) of Discounts and Premiums, Investments</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_AccretionAmortizationOfDiscountsAndPremiumsInvestments_lbl" xlink:role="http://www.xbrl.org/2009/role/negatedLabel">Net accretion of discounts on securities</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="srt_CumulativeEffectPeriodOfAdoptionAdjustedBalanceMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Adjusted Balance [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="srt_CumulativeEffectPeriodOfAdoptionAdjustedBalanceMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Cumulative Effect, Period of Adoption, Adjusted Balance [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_IncrementalCommonSharesAttributableToVestingOfRestrictedStockAwards_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Vesting of restricted stock awards</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_IncrementalCommonSharesAttributableToVestingOfRestrictedStockAwards_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Incremental Common Shares Attributable To Vesting Of Restricted Stock Awards</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_IncrementalCommonSharesAttributableToVestingOfRestrictedStockAwards_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Incremental common shares attributable to vesting of restricted stock awards.</link:label>
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          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="fisi_ScheduleOfShareBasedCompensationRestrictedStockUnitsAndPerformanceShareUnitsActivityTableTextBlock_lbl" xlink:role="http://www.xbrl.org/2003/role/documentation">Schedule of Share-based Compensation, Restricted Stock Units and Performance Share Units Activity [Table Text Block]</link:label>
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          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="srt_CumulativeEffectPeriodOfAdoptionDomain_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Cumulative Effect, Period of Adoption</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="srt_CumulativeEffectPeriodOfAdoptionDomain_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Cumulative Effect, Period of Adoption [Domain]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ResidentialMortgageMember_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Residential Real Estate Loans [Member]</link:label>
          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ResidentialMortgageMember_lbl" xlink:role="http://www.xbrl.org/2003/role/label">Residential Mortgage [Member]</link:label>
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          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_EmployeeServiceShareBasedCompensationTaxBenefitFromCompensationExpense_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Income tax benefit realized for compensation costs</link:label>
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          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_ProceedsFromMaturitiesPrepaymentsAndCallsOfAvailableForSaleSecurities_lbl" xlink:role="http://www.xbrl.org/2003/role/terseLabel">Proceeds from principal payments, maturities and calls on available for sale securities</link:label>
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          <link:label xml:lang="en-US" xlink:type="resource" xlink:label="us-gaap_DefinedBenefitPlanNetPeriodicBenefitCost_lbl" xlink:role="http://www.xbrl.org/2003/role/totalLabel">Net periodic benefit expense</link:label>
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  <xsd:element id="fisi_CardInterchangeIncome" name="CardInterchangeIncome" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="credit"/>
  <xsd:element id="fisi_FinancialReceivablesPercentageOfTotalLoans" name="FinancialReceivablesPercentageOfTotalLoans" type="dtr-types:percentItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false"/>
  <xsd:element id="fisi_CollateralizedMortgageBackedSecuritiesFederalNationalMortgageAssociationCertificatesAndObligationsFnmaMember" name="CollateralizedMortgageBackedSecuritiesFederalNationalMortgageAssociationCertificatesAndObligationsFnmaMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="fisi_CollateralizedMortgageObligationsMortgageBackedSecuritiesIssuedByPrivateEnterprisesMember" name="CollateralizedMortgageObligationsMortgageBackedSecuritiesIssuedByPrivateEnterprisesMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="fisi_ResidentialCollateralizedMortgageMember" name="ResidentialCollateralizedMortgageMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="fisi_OperatingLeaseRightOfUseAssetGross" name="OperatingLeaseRightOfUseAssetGross" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="debit"/>
  <xsd:element id="fisi_NoninterestIncomeInvestmentsInLimitedPartnerships" name="NoninterestIncomeInvestmentsInLimitedPartnerships" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="credit"/>
  <xsd:element id="fisi_ScheduleOfCreditLossExpenseBenefitForUnfundedCommitmentsTableTextBlock" name="ScheduleOfCreditLossExpenseBenefitForUnfundedCommitmentsTableTextBlock" type="dtr-types:textBlockItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false"/>
  <xsd:element id="fisi_FraudulentActivityPolicyTextBlock" name="FraudulentActivityPolicyTextBlock" type="dtr-types:textBlockItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false"/>
  <xsd:element id="fisi_LoanServicingRightsMember" name="LoanServicingRightsMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="fisi_HeldToMaturitySecuritiesNet" name="HeldToMaturitySecuritiesNet" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="debit"/>
  <xsd:element id="fisi_UnderwrittenPublicOfferingMember" name="UnderwrittenPublicOfferingMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="fisi_InternallyRatedHeldToMaturitySecurities" name="InternallyRatedHeldToMaturitySecurities" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="debit"/>
  <xsd:element id="fisi_DeposiRelatedChargedOffItemsRecoveriesExpense" name="DeposiRelatedChargedOffItemsRecoveriesExpense" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="debit"/>
  <xsd:element id="fisi_ChiefCommercialBankingOfficerMember" name="ChiefCommercialBankingOfficerMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="fisi_ScheduleOfClassificationOfRightOfUseAssetsAndLeaseLiabilitiesTableTextBlock" name="ScheduleOfClassificationOfRightOfUseAssetsAndLeaseLiabilitiesTableTextBlock" type="dtr-types:textBlockItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false"/>
  <xsd:element id="fisi_MortgageBackedSecuritiesAxis" name="MortgageBackedSecuritiesAxis" type="xbrli:stringItemType" substitutionGroup="xbrldt:dimensionItem" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="fisi_FairValueAssetsLevel1ToLevel2TransferAmount" name="FairValueAssetsLevel1ToLevel2TransferAmount" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="credit"/>
  <xsd:element id="fisi_AddedWeightedAverageLoansLife" name="AddedWeightedAverageLoansLife" type="xbrli:durationItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false"/>
  <xsd:element id="fisi_GainLossOnTaxCreditInvestments" name="GainLossOnTaxCreditInvestments" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="credit"/>
  <xsd:element id="fisi_OtherNoninterestExpensesMember" name="OtherNoninterestExpensesMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="fisi_MultifamilyMortgageMember" name="MultifamilyMortgageMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="fisi_OperationalAccountingAndReportingImpactsRelatedToCovidPandemicPolicyTextBlock" name="OperationalAccountingAndReportingImpactsRelatedToCovidPandemicPolicyTextBlock" type="dtr-types:textBlockItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false"/>
  <xsd:element id="fisi_ProceedsFromSaleOfDebtSecuritiesAvailableForSaleUsedToFundLosses" name="ProceedsFromSaleOfDebtSecuritiesAvailableForSaleUsedToFundLosses" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="debit"/>
  <xsd:element id="fisi_ChiefLegalOfficerMember" name="ChiefLegalOfficerMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="fisi_CollateralDependentLoanWithSpecificReserve" name="CollateralDependentLoanWithSpecificReserve" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="debit"/>
  <xsd:element id="fisi_InvestmentSecuritiesContinuousUnrealizedLossPositionLessThanTwelveMonthsFairValue" name="InvestmentSecuritiesContinuousUnrealizedLossPositionLessThanTwelveMonthsFairValue" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="debit"/>
  <xsd:element id="fisi_OtherFeesAndIncome" name="OtherFeesAndIncome" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="credit"/>
  <xsd:element id="fisi_OtherRealEstateOwnedOtherReceivableMember" name="OtherRealEstateOwnedOtherReceivableMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="fisi_CollateralDependentFinancingReceivableMember" name="CollateralDependentFinancingReceivableMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="fisi_CommercialCollateralizedMortgageMember" name="CommercialCollateralizedMortgageMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="fisi_OtherLiabilitiesMiscellaneous" name="OtherLiabilitiesMiscellaneous" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="credit"/>
  <xsd:element id="fisi_DerivativesEffectiveDate" name="DerivativesEffectiveDate" type="xbrli:dateItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false"/>
  <xsd:element id="fisi_MortgageBackedSecuritiesDomain" name="MortgageBackedSecuritiesDomain" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="fisi_Higher-YieldingAgencyWrappedInvestmentsMember" name="Higher-YieldingAgencyWrappedInvestmentsMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="fisi_PerformanceShareUnitsMember" name="PerformanceShareUnitsMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="fisi_InterestRateSwapTransactionTwoMember" name="InterestRateSwapTransactionTwoMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="fisi_SalariesAndEmployeeBenefitsMember" name="SalariesAndEmployeeBenefitsMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="fisi_SeriesB1EightPointFourEightPercentagePreferredStockMember" name="SeriesB1EightPointFourEightPercentagePreferredStockMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="fisi_ShareholdersEquityTable" name="ShareholdersEquityTable" type="xbrli:stringItemType" substitutionGroup="xbrldt:hypercubeItem" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="fisi_CollateralizedMortgageBackedSecuritiesGovernmentNationalMortgageAssociationCertificatesAndObligationsGnmaMember" name="CollateralizedMortgageBackedSecuritiesGovernmentNationalMortgageAssociationCertificatesAndObligationsGnmaMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="fisi_ConstructionMortgageMember" name="ConstructionMortgageMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="fisi_LoansHeldForSaleMember" name="LoansHeldForSaleMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="fisi_CashFlowReportingPolicyTextBlock" name="CashFlowReportingPolicyTextBlock" type="dtr-types:textBlockItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false"/>
  <xsd:element id="fisi_ProvisionForCreditLossesMember" name="ProvisionForCreditLossesMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="fisi_BenefitProvisionForCreditLosses" name="BenefitProvisionForCreditLosses" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="debit"/>
  <xsd:element id="fisi_ChiefMarketingOfficerMember" name="ChiefMarketingOfficerMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true"/>
  <xsd:element id="fisi_PercentageOfCommonSharesOutstanding" name="PercentageOfCommonSharesOutstanding" type="dtr-types:percentItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false"/>
</xsd:schema>
