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

<!--XBRL Document Created with the Workiva Platform-->
<!--Copyright 2026 Workiva-->
<!--r:019e88c3-c07d-7d10-81cb-88e60b6ddaaf,g:e2336880-bdc4-4bf1-8b5f-9296c3a4b7e9-->
<link:linkbase xmlns:link="http://www.xbrl.org/2003/linkbase" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xbrldt="http://xbrl.org/2005/xbrldt" xsi:schemaLocation="http://www.xbrl.org/2003/linkbase http://www.xbrl.org/2003/xbrl-linkbase-2003-12-31.xsd">
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/all" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#all"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#hypercube-dimension"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-default"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-domain"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/domain-member" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#domain-member"/>
  <link:roleRef roleURI="http://www.mdu.com/role/Cover" xlink:type="simple" xlink:href="mdu-20260618.xsd#Cover"/>
  <link:definitionLink xlink:role="http://www.mdu.com/role/Cover" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentInformationLineItems_019e88c3-c07d-70a6-b334-35ce6ad5f5ac" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_DocumentInformationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentInformationTable_019e88c3-c07d-7865-9578-2a46e22acb11" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_DocumentInformationTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_dei_DocumentInformationLineItems_019e88c3-c07d-70a6-b334-35ce6ad5f5ac" xlink:to="loc_dei_DocumentInformationTable_019e88c3-c07d-7865-9578-2a46e22acb11" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_019e88c3-c07d-7dab-b47c-f159d7835195" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_LegalEntityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_dei_DocumentInformationTable_019e88c3-c07d-7865-9578-2a46e22acb11" xlink:to="loc_dei_LegalEntityAxis_019e88c3-c07d-7dab-b47c-f159d7835195" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_019e88c3-c07d-7dab-b47c-f159d7835195_default" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_019e88c3-c07d-7dab-b47c-f159d7835195" xlink:to="loc_dei_EntityDomain_019e88c3-c07d-7dab-b47c-f159d7835195_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_019e88c3-c07d-7642-864d-4d37ec7d0cb4" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_019e88c3-c07d-7dab-b47c-f159d7835195" xlink:to="loc_dei_EntityDomain_019e88c3-c07d-7642-864d-4d37ec7d0cb4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_mdu_EBP004Member_019e88c3-c07d-768b-bfda-b2ad3b75960e" xlink:href="mdu-20260618.xsd#mdu_EBP004Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_019e88c3-c07d-7642-864d-4d37ec7d0cb4" xlink:to="loc_mdu_EBP004Member_019e88c3-c07d-768b-bfda-b2ad3b75960e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentType_019e88c3-c07d-7908-8b0b-09135e34edc8" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_DocumentType"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019e88c3-c07d-70a6-b334-35ce6ad5f5ac" xlink:to="loc_dei_DocumentType_019e88c3-c07d-7908-8b0b-09135e34edc8" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityRegistrantName_019e88c3-c07d-7049-9475-5d176e76da93" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityRegistrantName"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019e88c3-c07d-70a6-b334-35ce6ad5f5ac" xlink:to="loc_dei_EntityRegistrantName_019e88c3-c07d-7049-9475-5d176e76da93" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_AmendmentFlag_019e88c3-c07d-72f8-8b4b-0e7fdd9160c6" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_AmendmentFlag"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019e88c3-c07d-70a6-b334-35ce6ad5f5ac" xlink:to="loc_dei_AmendmentFlag_019e88c3-c07d-72f8-8b4b-0e7fdd9160c6" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityCentralIndexKey_019e88c3-c07d-7869-accb-9ffddab36a22" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityCentralIndexKey"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019e88c3-c07d-70a6-b334-35ce6ad5f5ac" xlink:to="loc_dei_EntityCentralIndexKey_019e88c3-c07d-7869-accb-9ffddab36a22" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.mdu.com/role/StatementsofNetAssetsAvailableforBenefits" xlink:type="simple" xlink:href="mdu-20260618.xsd#StatementsofNetAssetsAvailableforBenefits"/>
  <link:definitionLink xlink:role="http://www.mdu.com/role/StatementsofNetAssetsAvailableforBenefits" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap-ebp_EmployeeBenefitPlanStatementOfNetAssetAvailableForBenefitLineItems_019e88c3-c07d-76bd-8909-bd14e8346012" xlink:href="https://xbrl.fasb.org/us-gaap/2026/ebp/elts/us-gaap-ebp-2026.xsd#us-gaap-ebp_EmployeeBenefitPlanStatementOfNetAssetAvailableForBenefitLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap-ebp_EmployeeBenefitPlanStatementOfNetAssetAvailableForBenefitTable_019e88c3-c07d-7e84-9a02-1f21067587d4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/ebp/elts/us-gaap-ebp-2026.xsd#us-gaap-ebp_EmployeeBenefitPlanStatementOfNetAssetAvailableForBenefitTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap-ebp_EmployeeBenefitPlanStatementOfNetAssetAvailableForBenefitLineItems_019e88c3-c07d-76bd-8909-bd14e8346012" xlink:to="loc_us-gaap-ebp_EmployeeBenefitPlanStatementOfNetAssetAvailableForBenefitTable_019e88c3-c07d-7e84-9a02-1f21067587d4" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_019e88c3-c07d-7ae1-92ef-6053edd293ce" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_LegalEntityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap-ebp_EmployeeBenefitPlanStatementOfNetAssetAvailableForBenefitTable_019e88c3-c07d-7e84-9a02-1f21067587d4" xlink:to="loc_dei_LegalEntityAxis_019e88c3-c07d-7ae1-92ef-6053edd293ce" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_019e88c3-c07d-7ae1-92ef-6053edd293ce_default" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_019e88c3-c07d-7ae1-92ef-6053edd293ce" xlink:to="loc_dei_EntityDomain_019e88c3-c07d-7ae1-92ef-6053edd293ce_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_019e88c3-c07d-77e9-83b8-7704e202874c" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_019e88c3-c07d-7ae1-92ef-6053edd293ce" xlink:to="loc_dei_EntityDomain_019e88c3-c07d-77e9-83b8-7704e202874c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_mdu_EBP004Member_019e88c3-c07d-7f66-aa17-5aaad150abc4" xlink:href="mdu-20260618.xsd#mdu_EBP004Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_019e88c3-c07d-77e9-83b8-7704e202874c" xlink:to="loc_mdu_EBP004Member_019e88c3-c07d-7f66-aa17-5aaad150abc4" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap-ebp_EmployeeBenefitPlanAssetAbstract_019e88c3-c07d-7677-ab72-7fc1f4c04102" xlink:href="https://xbrl.fasb.org/us-gaap/2026/ebp/elts/us-gaap-ebp-2026.xsd#us-gaap-ebp_EmployeeBenefitPlanAssetAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap-ebp_EmployeeBenefitPlanStatementOfNetAssetAvailableForBenefitLineItems_019e88c3-c07d-76bd-8909-bd14e8346012" xlink:to="loc_us-gaap-ebp_EmployeeBenefitPlanAssetAbstract_019e88c3-c07d-7677-ab72-7fc1f4c04102" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap-ebp_EmployeeBenefitPlanInvestmentFairValueAbstract_019e88c3-c07d-7c62-8232-c6641eb756fd" xlink:href="https://xbrl.fasb.org/us-gaap/2026/ebp/elts/us-gaap-ebp-2026.xsd#us-gaap-ebp_EmployeeBenefitPlanInvestmentFairValueAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap-ebp_EmployeeBenefitPlanAssetAbstract_019e88c3-c07d-7677-ab72-7fc1f4c04102" xlink:to="loc_us-gaap-ebp_EmployeeBenefitPlanInvestmentFairValueAbstract_019e88c3-c07d-7c62-8232-c6641eb756fd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap-ebp_EmployeeBenefitPlanInvestmentExcludingPlanInterestInMasterTrustContractValue_019e88c3-c07d-7fce-ad54-9790cbec2312" xlink:href="https://xbrl.fasb.org/us-gaap/2026/ebp/elts/us-gaap-ebp-2026.xsd#us-gaap-ebp_EmployeeBenefitPlanInvestmentExcludingPlanInterestInMasterTrustContractValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap-ebp_EmployeeBenefitPlanInvestmentFairValueAbstract_019e88c3-c07d-7c62-8232-c6641eb756fd" xlink:to="loc_us-gaap-ebp_EmployeeBenefitPlanInvestmentExcludingPlanInterestInMasterTrustContractValue_019e88c3-c07d-7fce-ad54-9790cbec2312" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap-ebp_EmployeeBenefitPlanInvestmentExcludingPlanInterestInMasterTrustFairAndContractValue_019e88c3-c07d-7fdd-ac9f-32b6bb17601c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/ebp/elts/us-gaap-ebp-2026.xsd#us-gaap-ebp_EmployeeBenefitPlanInvestmentExcludingPlanInterestInMasterTrustFairAndContractValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap-ebp_EmployeeBenefitPlanInvestmentFairValueAbstract_019e88c3-c07d-7c62-8232-c6641eb756fd" xlink:to="loc_us-gaap-ebp_EmployeeBenefitPlanInvestmentExcludingPlanInterestInMasterTrustFairAndContractValue_019e88c3-c07d-7fdd-ac9f-32b6bb17601c" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap-ebp_EmployeeBenefitPlanInvestmentExcludingPlanInterestInMasterTrustFairValue_019e88c3-c07d-7ae9-bfdc-6cb1538b508b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/ebp/elts/us-gaap-ebp-2026.xsd#us-gaap-ebp_EmployeeBenefitPlanInvestmentExcludingPlanInterestInMasterTrustFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap-ebp_EmployeeBenefitPlanInvestmentFairValueAbstract_019e88c3-c07d-7c62-8232-c6641eb756fd" xlink:to="loc_us-gaap-ebp_EmployeeBenefitPlanInvestmentExcludingPlanInterestInMasterTrustFairValue_019e88c3-c07d-7ae9-bfdc-6cb1538b508b" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap-ebp_EmployeeBenefitPlanReceivableAbstract_019e88c3-c07d-7393-836d-67b84890e12b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/ebp/elts/us-gaap-ebp-2026.xsd#us-gaap-ebp_EmployeeBenefitPlanReceivableAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap-ebp_EmployeeBenefitPlanStatementOfNetAssetAvailableForBenefitLineItems_019e88c3-c07d-76bd-8909-bd14e8346012" xlink:to="loc_us-gaap-ebp_EmployeeBenefitPlanReceivableAbstract_019e88c3-c07d-7393-836d-67b84890e12b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap-ebp_EmployeeBenefitPlanEmployerContributionReceivable_019e88c3-c07d-7109-995f-93af97766dbb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/ebp/elts/us-gaap-ebp-2026.xsd#us-gaap-ebp_EmployeeBenefitPlanEmployerContributionReceivable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap-ebp_EmployeeBenefitPlanReceivableAbstract_019e88c3-c07d-7393-836d-67b84890e12b" xlink:to="loc_us-gaap-ebp_EmployeeBenefitPlanEmployerContributionReceivable_019e88c3-c07d-7109-995f-93af97766dbb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap-ebp_EmployeeBenefitPlanParticipantContributionReceivable_019e88c3-c07d-7d0f-872a-d8d523cf7883" xlink:href="https://xbrl.fasb.org/us-gaap/2026/ebp/elts/us-gaap-ebp-2026.xsd#us-gaap-ebp_EmployeeBenefitPlanParticipantContributionReceivable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap-ebp_EmployeeBenefitPlanReceivableAbstract_019e88c3-c07d-7393-836d-67b84890e12b" xlink:to="loc_us-gaap-ebp_EmployeeBenefitPlanParticipantContributionReceivable_019e88c3-c07d-7d0f-872a-d8d523cf7883" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap-ebp_EmployeeBenefitPlanNoteReceivableFromParticipant_019e88c3-c07d-732f-8912-69637629aac2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/ebp/elts/us-gaap-ebp-2026.xsd#us-gaap-ebp_EmployeeBenefitPlanNoteReceivableFromParticipant"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap-ebp_EmployeeBenefitPlanReceivableAbstract_019e88c3-c07d-7393-836d-67b84890e12b" xlink:to="loc_us-gaap-ebp_EmployeeBenefitPlanNoteReceivableFromParticipant_019e88c3-c07d-732f-8912-69637629aac2" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap-ebp_EmployeeBenefitPlanInvestmentIncomeReceivable_019e88c3-c07d-7453-9733-3b46315e0789" xlink:href="https://xbrl.fasb.org/us-gaap/2026/ebp/elts/us-gaap-ebp-2026.xsd#us-gaap-ebp_EmployeeBenefitPlanInvestmentIncomeReceivable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap-ebp_EmployeeBenefitPlanReceivableAbstract_019e88c3-c07d-7393-836d-67b84890e12b" xlink:to="loc_us-gaap-ebp_EmployeeBenefitPlanInvestmentIncomeReceivable_019e88c3-c07d-7453-9733-3b46315e0789" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap-ebp_EmployeeBenefitPlanOtherReceivable_019e88c3-c07d-79cd-be8a-54aaeb091490" xlink:href="https://xbrl.fasb.org/us-gaap/2026/ebp/elts/us-gaap-ebp-2026.xsd#us-gaap-ebp_EmployeeBenefitPlanOtherReceivable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap-ebp_EmployeeBenefitPlanReceivableAbstract_019e88c3-c07d-7393-836d-67b84890e12b" xlink:to="loc_us-gaap-ebp_EmployeeBenefitPlanOtherReceivable_019e88c3-c07d-79cd-be8a-54aaeb091490" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap-ebp_EmployeeBenefitPlanReceivable_019e88c3-c07d-747f-9561-ec7214143840" xlink:href="https://xbrl.fasb.org/us-gaap/2026/ebp/elts/us-gaap-ebp-2026.xsd#us-gaap-ebp_EmployeeBenefitPlanReceivable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap-ebp_EmployeeBenefitPlanReceivableAbstract_019e88c3-c07d-7393-836d-67b84890e12b" xlink:to="loc_us-gaap-ebp_EmployeeBenefitPlanReceivable_019e88c3-c07d-747f-9561-ec7214143840" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap-ebp_EmployeeBenefitPlanCash_019e88c3-c07d-764b-b2e1-321ea47e2fd6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/ebp/elts/us-gaap-ebp-2026.xsd#us-gaap-ebp_EmployeeBenefitPlanCash"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap-ebp_EmployeeBenefitPlanStatementOfNetAssetAvailableForBenefitLineItems_019e88c3-c07d-76bd-8909-bd14e8346012" xlink:to="loc_us-gaap-ebp_EmployeeBenefitPlanCash_019e88c3-c07d-764b-b2e1-321ea47e2fd6" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap-ebp_EmployeeBenefitPlanNetAssetAvailableForBenefit_019e88c3-c07d-7491-82c4-8fe7e41a4f19" xlink:href="https://xbrl.fasb.org/us-gaap/2026/ebp/elts/us-gaap-ebp-2026.xsd#us-gaap-ebp_EmployeeBenefitPlanNetAssetAvailableForBenefit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap-ebp_EmployeeBenefitPlanStatementOfNetAssetAvailableForBenefitLineItems_019e88c3-c07d-76bd-8909-bd14e8346012" xlink:to="loc_us-gaap-ebp_EmployeeBenefitPlanNetAssetAvailableForBenefit_019e88c3-c07d-7491-82c4-8fe7e41a4f19" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.mdu.com/role/StatementofChangesinNetAssetsAvailableforBenefits" xlink:type="simple" xlink:href="mdu-20260618.xsd#StatementofChangesinNetAssetsAvailableforBenefits"/>
  <link:definitionLink xlink:role="http://www.mdu.com/role/StatementofChangesinNetAssetsAvailableforBenefits" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap-ebp_EmployeeBenefitPlanStatementOfChangeInNetAssetAvailableForBenefitLineItems_019e88c3-c07d-7a82-a553-d6cec6a16b23" xlink:href="https://xbrl.fasb.org/us-gaap/2026/ebp/elts/us-gaap-ebp-2026.xsd#us-gaap-ebp_EmployeeBenefitPlanStatementOfChangeInNetAssetAvailableForBenefitLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap-ebp_EmployeeBenefitPlanStatementOfChangeInNetAssetAvailableForBenefitTable_019e88c3-c07d-756a-8bf2-974f03adb84b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/ebp/elts/us-gaap-ebp-2026.xsd#us-gaap-ebp_EmployeeBenefitPlanStatementOfChangeInNetAssetAvailableForBenefitTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap-ebp_EmployeeBenefitPlanStatementOfChangeInNetAssetAvailableForBenefitLineItems_019e88c3-c07d-7a82-a553-d6cec6a16b23" xlink:to="loc_us-gaap-ebp_EmployeeBenefitPlanStatementOfChangeInNetAssetAvailableForBenefitTable_019e88c3-c07d-756a-8bf2-974f03adb84b" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_019e88c3-c07d-7617-9e5f-4c86cd4a2e27" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_LegalEntityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap-ebp_EmployeeBenefitPlanStatementOfChangeInNetAssetAvailableForBenefitTable_019e88c3-c07d-756a-8bf2-974f03adb84b" xlink:to="loc_dei_LegalEntityAxis_019e88c3-c07d-7617-9e5f-4c86cd4a2e27" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_019e88c3-c07d-7617-9e5f-4c86cd4a2e27_default" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_019e88c3-c07d-7617-9e5f-4c86cd4a2e27" xlink:to="loc_dei_EntityDomain_019e88c3-c07d-7617-9e5f-4c86cd4a2e27_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_019e88c3-c07d-7ed0-ae88-5d51dfa04d3b" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_019e88c3-c07d-7617-9e5f-4c86cd4a2e27" xlink:to="loc_dei_EntityDomain_019e88c3-c07d-7ed0-ae88-5d51dfa04d3b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_mdu_EBP004Member_019e88c3-c07d-7a46-95c2-a7b6a807214a" xlink:href="mdu-20260618.xsd#mdu_EBP004Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_019e88c3-c07d-7ed0-ae88-5d51dfa04d3b" xlink:to="loc_mdu_EBP004Member_019e88c3-c07d-7a46-95c2-a7b6a807214a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap-ebp_EmployeeBenefitPlanChangeInNetAssetAvailableForBenefitIncreaseAbstract_019e88c3-c07d-70c7-aad5-926e7241ba0e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/ebp/elts/us-gaap-ebp-2026.xsd#us-gaap-ebp_EmployeeBenefitPlanChangeInNetAssetAvailableForBenefitIncreaseAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap-ebp_EmployeeBenefitPlanStatementOfChangeInNetAssetAvailableForBenefitLineItems_019e88c3-c07d-7a82-a553-d6cec6a16b23" xlink:to="loc_us-gaap-ebp_EmployeeBenefitPlanChangeInNetAssetAvailableForBenefitIncreaseAbstract_019e88c3-c07d-70c7-aad5-926e7241ba0e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap-ebp_EmployeeBenefitPlanChangeInNetAssetAvailableForBenefitIncreaseDecreaseForIncomeLossOnInvestmentAbstract_019e88c3-c07d-76b5-af27-b2caf6d284f5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/ebp/elts/us-gaap-ebp-2026.xsd#us-gaap-ebp_EmployeeBenefitPlanChangeInNetAssetAvailableForBenefitIncreaseDecreaseForIncomeLossOnInvestmentAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap-ebp_EmployeeBenefitPlanChangeInNetAssetAvailableForBenefitIncreaseAbstract_019e88c3-c07d-70c7-aad5-926e7241ba0e" xlink:to="loc_us-gaap-ebp_EmployeeBenefitPlanChangeInNetAssetAvailableForBenefitIncreaseDecreaseForIncomeLossOnInvestmentAbstract_019e88c3-c07d-76b5-af27-b2caf6d284f5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap-ebp_EmployeeBenefitPlanChangeInNetAssetAvailableForBenefitIncreaseForDividendIncomeOnInvestment_019e88c3-c07d-7fab-9fb4-1097a834f734" xlink:href="https://xbrl.fasb.org/us-gaap/2026/ebp/elts/us-gaap-ebp-2026.xsd#us-gaap-ebp_EmployeeBenefitPlanChangeInNetAssetAvailableForBenefitIncreaseForDividendIncomeOnInvestment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap-ebp_EmployeeBenefitPlanChangeInNetAssetAvailableForBenefitIncreaseDecreaseForIncomeLossOnInvestmentAbstract_019e88c3-c07d-76b5-af27-b2caf6d284f5" xlink:to="loc_us-gaap-ebp_EmployeeBenefitPlanChangeInNetAssetAvailableForBenefitIncreaseForDividendIncomeOnInvestment_019e88c3-c07d-7fab-9fb4-1097a834f734" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap-ebp_EmployeeBenefitPlanChangeInNetAssetAvailableForBenefitIncreaseForInterestAndDividendIncomeOnInvestment_019e88c3-c07d-7569-9e5b-d9edfd5dc44f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/ebp/elts/us-gaap-ebp-2026.xsd#us-gaap-ebp_EmployeeBenefitPlanChangeInNetAssetAvailableForBenefitIncreaseForInterestAndDividendIncomeOnInvestment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap-ebp_EmployeeBenefitPlanChangeInNetAssetAvailableForBenefitIncreaseDecreaseForIncomeLossOnInvestmentAbstract_019e88c3-c07d-76b5-af27-b2caf6d284f5" xlink:to="loc_us-gaap-ebp_EmployeeBenefitPlanChangeInNetAssetAvailableForBenefitIncreaseForInterestAndDividendIncomeOnInvestment_019e88c3-c07d-7569-9e5b-d9edfd5dc44f" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap-ebp_EmployeeBenefitPlanChangeInNetAssetAvailableForBenefitIncreaseDecreaseForGainLossOnInvestment_019e88c3-c07d-78f8-b7f4-89bead3a0453" xlink:href="https://xbrl.fasb.org/us-gaap/2026/ebp/elts/us-gaap-ebp-2026.xsd#us-gaap-ebp_EmployeeBenefitPlanChangeInNetAssetAvailableForBenefitIncreaseDecreaseForGainLossOnInvestment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap-ebp_EmployeeBenefitPlanChangeInNetAssetAvailableForBenefitIncreaseDecreaseForIncomeLossOnInvestmentAbstract_019e88c3-c07d-76b5-af27-b2caf6d284f5" xlink:to="loc_us-gaap-ebp_EmployeeBenefitPlanChangeInNetAssetAvailableForBenefitIncreaseDecreaseForGainLossOnInvestment_019e88c3-c07d-78f8-b7f4-89bead3a0453" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap-ebp_EmployeeBenefitPlanChangeInNetAssetAvailableForBenefitIncreaseDecreaseForIncomeLossOnInvestment_019e88c3-c07d-78fa-817b-516f46b42cc1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/ebp/elts/us-gaap-ebp-2026.xsd#us-gaap-ebp_EmployeeBenefitPlanChangeInNetAssetAvailableForBenefitIncreaseDecreaseForIncomeLossOnInvestment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap-ebp_EmployeeBenefitPlanChangeInNetAssetAvailableForBenefitIncreaseDecreaseForIncomeLossOnInvestmentAbstract_019e88c3-c07d-76b5-af27-b2caf6d284f5" xlink:to="loc_us-gaap-ebp_EmployeeBenefitPlanChangeInNetAssetAvailableForBenefitIncreaseDecreaseForIncomeLossOnInvestment_019e88c3-c07d-78fa-817b-516f46b42cc1" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap-ebp_EmployeeBenefitPlanChangeInNetAssetAvailableForBenefitIncreaseForInterestIncomeOnNoteReceivableFromParticipant_019e88c3-c07d-76c3-9007-8b3b069efa76" xlink:href="https://xbrl.fasb.org/us-gaap/2026/ebp/elts/us-gaap-ebp-2026.xsd#us-gaap-ebp_EmployeeBenefitPlanChangeInNetAssetAvailableForBenefitIncreaseForInterestIncomeOnNoteReceivableFromParticipant"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap-ebp_EmployeeBenefitPlanChangeInNetAssetAvailableForBenefitIncreaseAbstract_019e88c3-c07d-70c7-aad5-926e7241ba0e" xlink:to="loc_us-gaap-ebp_EmployeeBenefitPlanChangeInNetAssetAvailableForBenefitIncreaseForInterestIncomeOnNoteReceivableFromParticipant_019e88c3-c07d-76c3-9007-8b3b069efa76" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap-ebp_EmployeeBenefitPlanChangeInNetAssetAvailableForBenefitIncreaseForContributionAbstract_019e88c3-c07d-78c6-8e57-055e1b2aaf31" xlink:href="https://xbrl.fasb.org/us-gaap/2026/ebp/elts/us-gaap-ebp-2026.xsd#us-gaap-ebp_EmployeeBenefitPlanChangeInNetAssetAvailableForBenefitIncreaseForContributionAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap-ebp_EmployeeBenefitPlanChangeInNetAssetAvailableForBenefitIncreaseAbstract_019e88c3-c07d-70c7-aad5-926e7241ba0e" xlink:to="loc_us-gaap-ebp_EmployeeBenefitPlanChangeInNetAssetAvailableForBenefitIncreaseForContributionAbstract_019e88c3-c07d-78c6-8e57-055e1b2aaf31" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap-ebp_EmployeeBenefitPlanChangeInNetAssetAvailableForBenefitIncreaseForEmployerContributionCash_019e88c3-c07d-7b89-8cab-fade60833c0b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/ebp/elts/us-gaap-ebp-2026.xsd#us-gaap-ebp_EmployeeBenefitPlanChangeInNetAssetAvailableForBenefitIncreaseForEmployerContributionCash"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap-ebp_EmployeeBenefitPlanChangeInNetAssetAvailableForBenefitIncreaseForContributionAbstract_019e88c3-c07d-78c6-8e57-055e1b2aaf31" xlink:to="loc_us-gaap-ebp_EmployeeBenefitPlanChangeInNetAssetAvailableForBenefitIncreaseForEmployerContributionCash_019e88c3-c07d-7b89-8cab-fade60833c0b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap-ebp_EmployeeBenefitPlanChangeInNetAssetAvailableForBenefitIncreaseForParticipantContributionExcludingRollover_019e88c3-c07d-7fc6-ba0a-7eddba00301e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/ebp/elts/us-gaap-ebp-2026.xsd#us-gaap-ebp_EmployeeBenefitPlanChangeInNetAssetAvailableForBenefitIncreaseForParticipantContributionExcludingRollover"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap-ebp_EmployeeBenefitPlanChangeInNetAssetAvailableForBenefitIncreaseForContributionAbstract_019e88c3-c07d-78c6-8e57-055e1b2aaf31" xlink:to="loc_us-gaap-ebp_EmployeeBenefitPlanChangeInNetAssetAvailableForBenefitIncreaseForParticipantContributionExcludingRollover_019e88c3-c07d-7fc6-ba0a-7eddba00301e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap-ebp_EmployeeBenefitPlanChangeInNetAssetAvailableForBenefitIncreaseForParticipantContributionRollover_019e88c3-c07d-7719-add9-3eae610216ee" xlink:href="https://xbrl.fasb.org/us-gaap/2026/ebp/elts/us-gaap-ebp-2026.xsd#us-gaap-ebp_EmployeeBenefitPlanChangeInNetAssetAvailableForBenefitIncreaseForParticipantContributionRollover"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap-ebp_EmployeeBenefitPlanChangeInNetAssetAvailableForBenefitIncreaseForContributionAbstract_019e88c3-c07d-78c6-8e57-055e1b2aaf31" xlink:to="loc_us-gaap-ebp_EmployeeBenefitPlanChangeInNetAssetAvailableForBenefitIncreaseForParticipantContributionRollover_019e88c3-c07d-7719-add9-3eae610216ee" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap-ebp_EmployeeBenefitPlanChangeInNetAssetAvailableForBenefitIncreaseForContribution_019e88c3-c07d-7937-b8cb-a693f4df24b1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/ebp/elts/us-gaap-ebp-2026.xsd#us-gaap-ebp_EmployeeBenefitPlanChangeInNetAssetAvailableForBenefitIncreaseForContribution"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap-ebp_EmployeeBenefitPlanChangeInNetAssetAvailableForBenefitIncreaseForContributionAbstract_019e88c3-c07d-78c6-8e57-055e1b2aaf31" xlink:to="loc_us-gaap-ebp_EmployeeBenefitPlanChangeInNetAssetAvailableForBenefitIncreaseForContribution_019e88c3-c07d-7937-b8cb-a693f4df24b1" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap-ebp_EmployeeBenefitPlanChangeInNetAssetAvailableForBenefitIncrease_019e88c3-c07d-7e9f-9d09-043b652d6b88" xlink:href="https://xbrl.fasb.org/us-gaap/2026/ebp/elts/us-gaap-ebp-2026.xsd#us-gaap-ebp_EmployeeBenefitPlanChangeInNetAssetAvailableForBenefitIncrease"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap-ebp_EmployeeBenefitPlanChangeInNetAssetAvailableForBenefitIncreaseAbstract_019e88c3-c07d-70c7-aad5-926e7241ba0e" xlink:to="loc_us-gaap-ebp_EmployeeBenefitPlanChangeInNetAssetAvailableForBenefitIncrease_019e88c3-c07d-7e9f-9d09-043b652d6b88" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap-ebp_EmployeeBenefitPlanChangeInNetAssetAvailableForBenefitDecreaseAbstract_019e88c3-c07d-7245-9fc7-cb663e0605e4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/ebp/elts/us-gaap-ebp-2026.xsd#us-gaap-ebp_EmployeeBenefitPlanChangeInNetAssetAvailableForBenefitDecreaseAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap-ebp_EmployeeBenefitPlanStatementOfChangeInNetAssetAvailableForBenefitLineItems_019e88c3-c07d-7a82-a553-d6cec6a16b23" xlink:to="loc_us-gaap-ebp_EmployeeBenefitPlanChangeInNetAssetAvailableForBenefitDecreaseAbstract_019e88c3-c07d-7245-9fc7-cb663e0605e4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap-ebp_EmployeeBenefitPlanChangeInNetAssetAvailableForBenefitDecreaseForPaymentToParticipant_019e88c3-c07d-7453-9f6d-651c7e8bf7bb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/ebp/elts/us-gaap-ebp-2026.xsd#us-gaap-ebp_EmployeeBenefitPlanChangeInNetAssetAvailableForBenefitDecreaseForPaymentToParticipant"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap-ebp_EmployeeBenefitPlanChangeInNetAssetAvailableForBenefitDecreaseAbstract_019e88c3-c07d-7245-9fc7-cb663e0605e4" xlink:to="loc_us-gaap-ebp_EmployeeBenefitPlanChangeInNetAssetAvailableForBenefitDecreaseForPaymentToParticipant_019e88c3-c07d-7453-9f6d-651c7e8bf7bb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap-ebp_EmployeeBenefitPlanChangeInNetAssetAvailableForBenefitDecreaseForAdministrativeExpense_019e88c3-c07d-7a66-a78c-f3ed133cf02d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/ebp/elts/us-gaap-ebp-2026.xsd#us-gaap-ebp_EmployeeBenefitPlanChangeInNetAssetAvailableForBenefitDecreaseForAdministrativeExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap-ebp_EmployeeBenefitPlanChangeInNetAssetAvailableForBenefitDecreaseAbstract_019e88c3-c07d-7245-9fc7-cb663e0605e4" xlink:to="loc_us-gaap-ebp_EmployeeBenefitPlanChangeInNetAssetAvailableForBenefitDecreaseForAdministrativeExpense_019e88c3-c07d-7a66-a78c-f3ed133cf02d" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap-ebp_EmployeeBenefitPlanChangeInNetAssetAvailableForBenefitDecrease_019e88c3-c07d-747e-b99e-5d61560b72f9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/ebp/elts/us-gaap-ebp-2026.xsd#us-gaap-ebp_EmployeeBenefitPlanChangeInNetAssetAvailableForBenefitDecrease"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap-ebp_EmployeeBenefitPlanChangeInNetAssetAvailableForBenefitDecreaseAbstract_019e88c3-c07d-7245-9fc7-cb663e0605e4" xlink:to="loc_us-gaap-ebp_EmployeeBenefitPlanChangeInNetAssetAvailableForBenefitDecrease_019e88c3-c07d-747e-b99e-5d61560b72f9" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap-ebp_EmployeeBenefitPlanChangeInNetAssetAvailableForBenefitIncreaseDecrease_019e88c3-c07d-788f-acef-8041e6bc735a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/ebp/elts/us-gaap-ebp-2026.xsd#us-gaap-ebp_EmployeeBenefitPlanChangeInNetAssetAvailableForBenefitIncreaseDecrease"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap-ebp_EmployeeBenefitPlanStatementOfChangeInNetAssetAvailableForBenefitLineItems_019e88c3-c07d-7a82-a553-d6cec6a16b23" xlink:to="loc_us-gaap-ebp_EmployeeBenefitPlanChangeInNetAssetAvailableForBenefitIncreaseDecrease_019e88c3-c07d-788f-acef-8041e6bc735a" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap-ebp_EmployeeBenefitPlanChangeInNetAssetAvailableForBenefitTransferToFromExternalPlan_019e88c3-c07d-750c-a529-2ecf12488681" xlink:href="https://xbrl.fasb.org/us-gaap/2026/ebp/elts/us-gaap-ebp-2026.xsd#us-gaap-ebp_EmployeeBenefitPlanChangeInNetAssetAvailableForBenefitTransferToFromExternalPlan"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap-ebp_EmployeeBenefitPlanStatementOfChangeInNetAssetAvailableForBenefitLineItems_019e88c3-c07d-7a82-a553-d6cec6a16b23" xlink:to="loc_us-gaap-ebp_EmployeeBenefitPlanChangeInNetAssetAvailableForBenefitTransferToFromExternalPlan_019e88c3-c07d-750c-a529-2ecf12488681" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_mdu_EBPChangeInNetAssetAvailableForBenefitIncludingPlanTransfersIncreaseDecrease_019e88c3-c07d-7ee9-a140-132c0f8450c4" xlink:href="mdu-20260618.xsd#mdu_EBPChangeInNetAssetAvailableForBenefitIncludingPlanTransfersIncreaseDecrease"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap-ebp_EmployeeBenefitPlanStatementOfChangeInNetAssetAvailableForBenefitLineItems_019e88c3-c07d-7a82-a553-d6cec6a16b23" xlink:to="loc_mdu_EBPChangeInNetAssetAvailableForBenefitIncludingPlanTransfersIncreaseDecrease_019e88c3-c07d-7ee9-a140-132c0f8450c4" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap-ebp_EmployeeBenefitPlanNetAssetAvailableForBenefit_019e88c3-c07d-7699-885b-0a2977471174" xlink:href="https://xbrl.fasb.org/us-gaap/2026/ebp/elts/us-gaap-ebp-2026.xsd#us-gaap-ebp_EmployeeBenefitPlanNetAssetAvailableForBenefit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap-ebp_EmployeeBenefitPlanStatementOfChangeInNetAssetAvailableForBenefitLineItems_019e88c3-c07d-7a82-a553-d6cec6a16b23" xlink:to="loc_us-gaap-ebp_EmployeeBenefitPlanNetAssetAvailableForBenefit_019e88c3-c07d-7699-885b-0a2977471174" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap-ebp_EmployeeBenefitPlanNetAssetAvailableForBenefit_019e88c3-c07d-7ca9-9f0e-a17d813d3f3d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/ebp/elts/us-gaap-ebp-2026.xsd#us-gaap-ebp_EmployeeBenefitPlanNetAssetAvailableForBenefit"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.mdu.com/role/DescriptionofthePlan" xlink:type="simple" xlink:href="mdu-20260618.xsd#DescriptionofthePlan"/>
  <link:definitionLink xlink:role="http://www.mdu.com/role/DescriptionofthePlan" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap-ebp_EmployeeBenefitPlanDescriptionOfPlanLineItems_019e88c3-c07d-78c8-8e0d-5b799df8c0ba" xlink:href="https://xbrl.fasb.org/us-gaap/2026/ebp/elts/us-gaap-ebp-2026.xsd#us-gaap-ebp_EmployeeBenefitPlanDescriptionOfPlanLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap-ebp_EmployeeBenefitPlanDescriptionOfPlanTable_019e88c3-c07d-73fb-990a-50768a180cf8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/ebp/elts/us-gaap-ebp-2026.xsd#us-gaap-ebp_EmployeeBenefitPlanDescriptionOfPlanTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap-ebp_EmployeeBenefitPlanDescriptionOfPlanLineItems_019e88c3-c07d-78c8-8e0d-5b799df8c0ba" xlink:to="loc_us-gaap-ebp_EmployeeBenefitPlanDescriptionOfPlanTable_019e88c3-c07d-73fb-990a-50768a180cf8" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_019e88c3-c07d-7520-a0e5-a126fe18eb5f" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_LegalEntityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap-ebp_EmployeeBenefitPlanDescriptionOfPlanTable_019e88c3-c07d-73fb-990a-50768a180cf8" xlink:to="loc_dei_LegalEntityAxis_019e88c3-c07d-7520-a0e5-a126fe18eb5f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_019e88c3-c07d-7520-a0e5-a126fe18eb5f_default" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_019e88c3-c07d-7520-a0e5-a126fe18eb5f" xlink:to="loc_dei_EntityDomain_019e88c3-c07d-7520-a0e5-a126fe18eb5f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_019e88c3-c07d-7603-bd4f-3aa13f497265" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_019e88c3-c07d-7520-a0e5-a126fe18eb5f" xlink:to="loc_dei_EntityDomain_019e88c3-c07d-7603-bd4f-3aa13f497265" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_mdu_EBP004Member_019e88c3-c07d-791e-b681-7a9babbc426b" xlink:href="mdu-20260618.xsd#mdu_EBP004Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_019e88c3-c07d-7603-bd4f-3aa13f497265" xlink:to="loc_mdu_EBP004Member_019e88c3-c07d-791e-b681-7a9babbc426b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap-ebp_EmployeeBenefitPlanDescriptionOfPlanTextBlock_019e88c3-c07d-74e6-8dda-cd91c3502a91" xlink:href="https://xbrl.fasb.org/us-gaap/2026/ebp/elts/us-gaap-ebp-2026.xsd#us-gaap-ebp_EmployeeBenefitPlanDescriptionOfPlanTextBlock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap-ebp_EmployeeBenefitPlanDescriptionOfPlanLineItems_019e88c3-c07d-78c8-8e0d-5b799df8c0ba" xlink:to="loc_us-gaap-ebp_EmployeeBenefitPlanDescriptionOfPlanTextBlock_019e88c3-c07d-74e6-8dda-cd91c3502a91" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.mdu.com/role/SummaryofSignificantAccountingPolicies" xlink:type="simple" xlink:href="mdu-20260618.xsd#SummaryofSignificantAccountingPolicies"/>
  <link:definitionLink xlink:role="http://www.mdu.com/role/SummaryofSignificantAccountingPolicies" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap-ebp_EmployeeBenefitPlanAccountingPolicyLineItems_019e88c3-c07d-7eb2-98a8-12674b120952" xlink:href="https://xbrl.fasb.org/us-gaap/2026/ebp/elts/us-gaap-ebp-2026.xsd#us-gaap-ebp_EmployeeBenefitPlanAccountingPolicyLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap-ebp_EmployeeBenefitPlanAccountingPolicyTable_019e88c3-c07d-78cf-892a-9b38aaf09f5a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/ebp/elts/us-gaap-ebp-2026.xsd#us-gaap-ebp_EmployeeBenefitPlanAccountingPolicyTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap-ebp_EmployeeBenefitPlanAccountingPolicyLineItems_019e88c3-c07d-7eb2-98a8-12674b120952" xlink:to="loc_us-gaap-ebp_EmployeeBenefitPlanAccountingPolicyTable_019e88c3-c07d-78cf-892a-9b38aaf09f5a" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_019e88c3-c07d-72d4-b3e5-a2e6e693e114" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_LegalEntityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap-ebp_EmployeeBenefitPlanAccountingPolicyTable_019e88c3-c07d-78cf-892a-9b38aaf09f5a" xlink:to="loc_dei_LegalEntityAxis_019e88c3-c07d-72d4-b3e5-a2e6e693e114" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_019e88c3-c07d-72d4-b3e5-a2e6e693e114_default" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_019e88c3-c07d-72d4-b3e5-a2e6e693e114" xlink:to="loc_dei_EntityDomain_019e88c3-c07d-72d4-b3e5-a2e6e693e114_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_019e88c3-c07d-73e4-b724-f66af8b13fe4" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_019e88c3-c07d-72d4-b3e5-a2e6e693e114" xlink:to="loc_dei_EntityDomain_019e88c3-c07d-73e4-b724-f66af8b13fe4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_mdu_EBP004Member_019e88c3-c07d-7756-8179-638e2367e92c" xlink:href="mdu-20260618.xsd#mdu_EBP004Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_019e88c3-c07d-73e4-b724-f66af8b13fe4" xlink:to="loc_mdu_EBP004Member_019e88c3-c07d-7756-8179-638e2367e92c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap-ebp_EmployeeBenefitPlanSummaryOfAccountingPolicyTextBlock_019e88c3-c07d-7833-8d22-1f06081fc22a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/ebp/elts/us-gaap-ebp-2026.xsd#us-gaap-ebp_EmployeeBenefitPlanSummaryOfAccountingPolicyTextBlock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap-ebp_EmployeeBenefitPlanAccountingPolicyLineItems_019e88c3-c07d-7eb2-98a8-12674b120952" xlink:to="loc_us-gaap-ebp_EmployeeBenefitPlanSummaryOfAccountingPolicyTextBlock_019e88c3-c07d-7833-8d22-1f06081fc22a" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.mdu.com/role/InvestmentContractwithInsuranceCompany" xlink:type="simple" xlink:href="mdu-20260618.xsd#InvestmentContractwithInsuranceCompany"/>
  <link:definitionLink xlink:role="http://www.mdu.com/role/InvestmentContractwithInsuranceCompany" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap-ebp_EmployeeBenefitPlanFullyBenefitResponsiveInvestmentContractLineItems_019e88c3-c07d-79da-bb94-1da91220020f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/ebp/elts/us-gaap-ebp-2026.xsd#us-gaap-ebp_EmployeeBenefitPlanFullyBenefitResponsiveInvestmentContractLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap-ebp_EmployeeBenefitPlanFullyBenefitResponsiveInvestmentContractTable_019e88c3-c07d-7d8f-80c2-9b475de4d130" xlink:href="https://xbrl.fasb.org/us-gaap/2026/ebp/elts/us-gaap-ebp-2026.xsd#us-gaap-ebp_EmployeeBenefitPlanFullyBenefitResponsiveInvestmentContractTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap-ebp_EmployeeBenefitPlanFullyBenefitResponsiveInvestmentContractLineItems_019e88c3-c07d-79da-bb94-1da91220020f" xlink:to="loc_us-gaap-ebp_EmployeeBenefitPlanFullyBenefitResponsiveInvestmentContractTable_019e88c3-c07d-7d8f-80c2-9b475de4d130" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_019e88c3-c07d-729b-b38c-80fb5ebce590" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_LegalEntityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap-ebp_EmployeeBenefitPlanFullyBenefitResponsiveInvestmentContractTable_019e88c3-c07d-7d8f-80c2-9b475de4d130" xlink:to="loc_dei_LegalEntityAxis_019e88c3-c07d-729b-b38c-80fb5ebce590" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_019e88c3-c07d-729b-b38c-80fb5ebce590_default" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_019e88c3-c07d-729b-b38c-80fb5ebce590" xlink:to="loc_dei_EntityDomain_019e88c3-c07d-729b-b38c-80fb5ebce590_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_019e88c3-c07d-7cc5-a122-a289b19d83b0" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_019e88c3-c07d-729b-b38c-80fb5ebce590" xlink:to="loc_dei_EntityDomain_019e88c3-c07d-7cc5-a122-a289b19d83b0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_mdu_EBP004Member_019e88c3-c07d-7d08-bb21-07587124823c" xlink:href="mdu-20260618.xsd#mdu_EBP004Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_019e88c3-c07d-7cc5-a122-a289b19d83b0" xlink:to="loc_mdu_EBP004Member_019e88c3-c07d-7d08-bb21-07587124823c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_mdu_EBPInvestmentTextBlock_019e88c3-c07d-73d2-b0b2-9c4cf88e8379" xlink:href="mdu-20260618.xsd#mdu_EBPInvestmentTextBlock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap-ebp_EmployeeBenefitPlanFullyBenefitResponsiveInvestmentContractLineItems_019e88c3-c07d-79da-bb94-1da91220020f" xlink:to="loc_mdu_EBPInvestmentTextBlock_019e88c3-c07d-73d2-b0b2-9c4cf88e8379" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.mdu.com/role/FairValueMeasurements" xlink:type="simple" xlink:href="mdu-20260618.xsd#FairValueMeasurements"/>
  <link:definitionLink xlink:role="http://www.mdu.com/role/FairValueMeasurements" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap-ebp_EmployeeBenefitPlanInvestmentFairValueAndNavLineItems_019e88c3-c07d-77b9-99f1-136e6917419e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/ebp/elts/us-gaap-ebp-2026.xsd#us-gaap-ebp_EmployeeBenefitPlanInvestmentFairValueAndNavLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap-ebp_EmployeeBenefitPlanInvestmentFairValueAndNavTable_019e88c3-c07d-7abd-a891-76d0c94b7ffb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/ebp/elts/us-gaap-ebp-2026.xsd#us-gaap-ebp_EmployeeBenefitPlanInvestmentFairValueAndNavTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap-ebp_EmployeeBenefitPlanInvestmentFairValueAndNavLineItems_019e88c3-c07d-77b9-99f1-136e6917419e" xlink:to="loc_us-gaap-ebp_EmployeeBenefitPlanInvestmentFairValueAndNavTable_019e88c3-c07d-7abd-a891-76d0c94b7ffb" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_019e88c3-c07d-7343-a061-2eae553afe15" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_LegalEntityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap-ebp_EmployeeBenefitPlanInvestmentFairValueAndNavTable_019e88c3-c07d-7abd-a891-76d0c94b7ffb" xlink:to="loc_dei_LegalEntityAxis_019e88c3-c07d-7343-a061-2eae553afe15" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_019e88c3-c07d-7343-a061-2eae553afe15_default" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_019e88c3-c07d-7343-a061-2eae553afe15" xlink:to="loc_dei_EntityDomain_019e88c3-c07d-7343-a061-2eae553afe15_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_019e88c3-c07d-72f2-bb7c-c8636062a862" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_019e88c3-c07d-7343-a061-2eae553afe15" xlink:to="loc_dei_EntityDomain_019e88c3-c07d-72f2-bb7c-c8636062a862" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_mdu_EBP004Member_019e88c3-c07d-7b7e-bffd-b4c4e0c93625" xlink:href="mdu-20260618.xsd#mdu_EBP004Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_019e88c3-c07d-72f2-bb7c-c8636062a862" xlink:to="loc_mdu_EBP004Member_019e88c3-c07d-7b7e-bffd-b4c4e0c93625" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap-ebp_EmployeeBenefitPlanInvestmentFairValueAndNavTextBlock_019e88c3-c07d-7b8d-b7da-5b7fe6b568cc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/ebp/elts/us-gaap-ebp-2026.xsd#us-gaap-ebp_EmployeeBenefitPlanInvestmentFairValueAndNavTextBlock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap-ebp_EmployeeBenefitPlanInvestmentFairValueAndNavLineItems_019e88c3-c07d-77b9-99f1-136e6917419e" xlink:to="loc_us-gaap-ebp_EmployeeBenefitPlanInvestmentFairValueAndNavTextBlock_019e88c3-c07d-7b8d-b7da-5b7fe6b568cc" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.mdu.com/role/FederalIncomeTaxes" xlink:type="simple" xlink:href="mdu-20260618.xsd#FederalIncomeTaxes"/>
  <link:definitionLink xlink:role="http://www.mdu.com/role/FederalIncomeTaxes" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap-ebp_EmployeeBenefitPlanTaxStatusLineItems_019e88c3-c07d-7076-af33-8662ade5f822" xlink:href="https://xbrl.fasb.org/us-gaap/2026/ebp/elts/us-gaap-ebp-2026.xsd#us-gaap-ebp_EmployeeBenefitPlanTaxStatusLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap-ebp_EmployeeBenefitPlanTaxStatusTable_019e88c3-c07d-74f3-8d25-3af4b6a353be" xlink:href="https://xbrl.fasb.org/us-gaap/2026/ebp/elts/us-gaap-ebp-2026.xsd#us-gaap-ebp_EmployeeBenefitPlanTaxStatusTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap-ebp_EmployeeBenefitPlanTaxStatusLineItems_019e88c3-c07d-7076-af33-8662ade5f822" xlink:to="loc_us-gaap-ebp_EmployeeBenefitPlanTaxStatusTable_019e88c3-c07d-74f3-8d25-3af4b6a353be" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_019e88c3-c07d-77fe-9268-0805ecdc17e5" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_LegalEntityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap-ebp_EmployeeBenefitPlanTaxStatusTable_019e88c3-c07d-74f3-8d25-3af4b6a353be" xlink:to="loc_dei_LegalEntityAxis_019e88c3-c07d-77fe-9268-0805ecdc17e5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_019e88c3-c07d-77fe-9268-0805ecdc17e5_default" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_019e88c3-c07d-77fe-9268-0805ecdc17e5" xlink:to="loc_dei_EntityDomain_019e88c3-c07d-77fe-9268-0805ecdc17e5_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_019e88c3-c07d-7fba-aaf1-c30ab35e2c3d" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_019e88c3-c07d-77fe-9268-0805ecdc17e5" xlink:to="loc_dei_EntityDomain_019e88c3-c07d-7fba-aaf1-c30ab35e2c3d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_mdu_EBP004Member_019e88c3-c07d-7ec3-bce4-40b3dee98ef7" xlink:href="mdu-20260618.xsd#mdu_EBP004Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_019e88c3-c07d-7fba-aaf1-c30ab35e2c3d" xlink:to="loc_mdu_EBP004Member_019e88c3-c07d-7ec3-bce4-40b3dee98ef7" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap-ebp_EmployeeBenefitPlanTaxStatusTextBlock_019e88c3-c07d-711e-aef6-40e00af6bfa2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/ebp/elts/us-gaap-ebp-2026.xsd#us-gaap-ebp_EmployeeBenefitPlanTaxStatusTextBlock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap-ebp_EmployeeBenefitPlanTaxStatusLineItems_019e88c3-c07d-7076-af33-8662ade5f822" xlink:to="loc_us-gaap-ebp_EmployeeBenefitPlanTaxStatusTextBlock_019e88c3-c07d-711e-aef6-40e00af6bfa2" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.mdu.com/role/RelatedPartyandExemptPartyInInterestTransactions" xlink:type="simple" xlink:href="mdu-20260618.xsd#RelatedPartyandExemptPartyInInterestTransactions"/>
  <link:definitionLink xlink:role="http://www.mdu.com/role/RelatedPartyandExemptPartyInInterestTransactions" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap-ebp_EmployeeBenefitPlanRelatedPartyAndPartyInInterestTransactionsLineItems_019e88c3-c07d-732c-a12f-a3cb43c4f6a8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/ebp/elts/us-gaap-ebp-2026.xsd#us-gaap-ebp_EmployeeBenefitPlanRelatedPartyAndPartyInInterestTransactionsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap-ebp_EmployeeBenefitPlanRelatedPartyAndPartyInInterestTransactionsTable_019e88c3-c07d-75eb-9a26-de70a5d4c954" xlink:href="https://xbrl.fasb.org/us-gaap/2026/ebp/elts/us-gaap-ebp-2026.xsd#us-gaap-ebp_EmployeeBenefitPlanRelatedPartyAndPartyInInterestTransactionsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap-ebp_EmployeeBenefitPlanRelatedPartyAndPartyInInterestTransactionsLineItems_019e88c3-c07d-732c-a12f-a3cb43c4f6a8" xlink:to="loc_us-gaap-ebp_EmployeeBenefitPlanRelatedPartyAndPartyInInterestTransactionsTable_019e88c3-c07d-75eb-9a26-de70a5d4c954" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_019e88c3-c07d-7cc0-975f-3712add1bd48" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_LegalEntityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap-ebp_EmployeeBenefitPlanRelatedPartyAndPartyInInterestTransactionsTable_019e88c3-c07d-75eb-9a26-de70a5d4c954" xlink:to="loc_dei_LegalEntityAxis_019e88c3-c07d-7cc0-975f-3712add1bd48" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_019e88c3-c07d-7cc0-975f-3712add1bd48_default" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_019e88c3-c07d-7cc0-975f-3712add1bd48" xlink:to="loc_dei_EntityDomain_019e88c3-c07d-7cc0-975f-3712add1bd48_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_019e88c3-c07d-75f0-a329-eaa3d090b485" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_019e88c3-c07d-7cc0-975f-3712add1bd48" xlink:to="loc_dei_EntityDomain_019e88c3-c07d-75f0-a329-eaa3d090b485" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_mdu_EBP004Member_019e88c3-c07d-71ea-a8ce-99ca3fd8c15e" xlink:href="mdu-20260618.xsd#mdu_EBP004Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_019e88c3-c07d-75f0-a329-eaa3d090b485" xlink:to="loc_mdu_EBP004Member_019e88c3-c07d-71ea-a8ce-99ca3fd8c15e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap-ebp_EmployeeBenefitPlanRelatedPartyAndPartyInInterestTransactionsTextBlock_019e88c3-c07d-797c-8739-ee155f5a0f66" xlink:href="https://xbrl.fasb.org/us-gaap/2026/ebp/elts/us-gaap-ebp-2026.xsd#us-gaap-ebp_EmployeeBenefitPlanRelatedPartyAndPartyInInterestTransactionsTextBlock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap-ebp_EmployeeBenefitPlanRelatedPartyAndPartyInInterestTransactionsLineItems_019e88c3-c07d-732c-a12f-a3cb43c4f6a8" xlink:to="loc_us-gaap-ebp_EmployeeBenefitPlanRelatedPartyAndPartyInInterestTransactionsTextBlock_019e88c3-c07d-797c-8739-ee155f5a0f66" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.mdu.com/role/ReconciliationofFinancialStatementstoForm5500" xlink:type="simple" xlink:href="mdu-20260618.xsd#ReconciliationofFinancialStatementstoForm5500"/>
  <link:definitionLink xlink:role="http://www.mdu.com/role/ReconciliationofFinancialStatementstoForm5500" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap-ebp_EmployeeBenefitPlanReconciliationToForm5500LineItems_019e88c3-c07d-7c46-9e95-b57921b91c83" xlink:href="https://xbrl.fasb.org/us-gaap/2026/ebp/elts/us-gaap-ebp-2026.xsd#us-gaap-ebp_EmployeeBenefitPlanReconciliationToForm5500LineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap-ebp_EmployeeBenefitPlanReconciliationToForm5500Table_019e88c3-c07d-793d-9bc8-92c5efb4a243" xlink:href="https://xbrl.fasb.org/us-gaap/2026/ebp/elts/us-gaap-ebp-2026.xsd#us-gaap-ebp_EmployeeBenefitPlanReconciliationToForm5500Table"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap-ebp_EmployeeBenefitPlanReconciliationToForm5500LineItems_019e88c3-c07d-7c46-9e95-b57921b91c83" xlink:to="loc_us-gaap-ebp_EmployeeBenefitPlanReconciliationToForm5500Table_019e88c3-c07d-793d-9bc8-92c5efb4a243" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_019e88c3-c07d-740e-9f80-c7fd91537d29" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_LegalEntityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap-ebp_EmployeeBenefitPlanReconciliationToForm5500Table_019e88c3-c07d-793d-9bc8-92c5efb4a243" xlink:to="loc_dei_LegalEntityAxis_019e88c3-c07d-740e-9f80-c7fd91537d29" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_019e88c3-c07d-740e-9f80-c7fd91537d29_default" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_019e88c3-c07d-740e-9f80-c7fd91537d29" xlink:to="loc_dei_EntityDomain_019e88c3-c07d-740e-9f80-c7fd91537d29_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_019e88c3-c07d-7ec6-b21b-ac5825e06bcc" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_019e88c3-c07d-740e-9f80-c7fd91537d29" xlink:to="loc_dei_EntityDomain_019e88c3-c07d-7ec6-b21b-ac5825e06bcc" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_mdu_EBP004Member_019e88c3-c07d-7dc0-ad99-3591389d6c4c" xlink:href="mdu-20260618.xsd#mdu_EBP004Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_019e88c3-c07d-7ec6-b21b-ac5825e06bcc" xlink:to="loc_mdu_EBP004Member_019e88c3-c07d-7dc0-ad99-3591389d6c4c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap-ebp_EmployeeBenefitPlanReconciliationToForm5500TextBlock_019e88c3-c07d-7993-b65a-349378d906e8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/ebp/elts/us-gaap-ebp-2026.xsd#us-gaap-ebp_EmployeeBenefitPlanReconciliationToForm5500TextBlock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap-ebp_EmployeeBenefitPlanReconciliationToForm5500LineItems_019e88c3-c07d-7c46-9e95-b57921b91c83" xlink:to="loc_us-gaap-ebp_EmployeeBenefitPlanReconciliationToForm5500TextBlock_019e88c3-c07d-7993-b65a-349378d906e8" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.mdu.com/role/SubsequentEvents" xlink:type="simple" xlink:href="mdu-20260618.xsd#SubsequentEvents"/>
  <link:definitionLink xlink:role="http://www.mdu.com/role/SubsequentEvents" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap-ebp_EbpSubsequentEventLineItems_019e88c3-c07d-7c54-900a-40af8d7c4166" xlink:href="https://xbrl.fasb.org/us-gaap/2026/ebp/elts/us-gaap-ebp-2026.xsd#us-gaap-ebp_EbpSubsequentEventLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap-ebp_EbpSubsequentEventTable_019e88c3-c07d-7dbc-8833-1097f1b86e01" xlink:href="https://xbrl.fasb.org/us-gaap/2026/ebp/elts/us-gaap-ebp-2026.xsd#us-gaap-ebp_EbpSubsequentEventTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap-ebp_EbpSubsequentEventLineItems_019e88c3-c07d-7c54-900a-40af8d7c4166" xlink:to="loc_us-gaap-ebp_EbpSubsequentEventTable_019e88c3-c07d-7dbc-8833-1097f1b86e01" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_019e88c3-c07d-7b4d-9905-500ff66f8cb0" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_LegalEntityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap-ebp_EbpSubsequentEventTable_019e88c3-c07d-7dbc-8833-1097f1b86e01" xlink:to="loc_dei_LegalEntityAxis_019e88c3-c07d-7b4d-9905-500ff66f8cb0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_019e88c3-c07d-7b4d-9905-500ff66f8cb0_default" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_019e88c3-c07d-7b4d-9905-500ff66f8cb0" xlink:to="loc_dei_EntityDomain_019e88c3-c07d-7b4d-9905-500ff66f8cb0_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_019e88c3-c07d-7db6-bbc7-2f27199abada" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_019e88c3-c07d-7b4d-9905-500ff66f8cb0" xlink:to="loc_dei_EntityDomain_019e88c3-c07d-7db6-bbc7-2f27199abada" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_mdu_EBP004Member_019e88c3-c07d-7527-ab4b-086415fa841c" xlink:href="mdu-20260618.xsd#mdu_EBP004Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_019e88c3-c07d-7db6-bbc7-2f27199abada" xlink:to="loc_mdu_EBP004Member_019e88c3-c07d-7527-ab4b-086415fa841c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap-ebp_EmployeeBenefitPlanSubsequentEventTextBlock_019e88c3-c07d-75b9-b0e7-70a46ed0509b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/ebp/elts/us-gaap-ebp-2026.xsd#us-gaap-ebp_EmployeeBenefitPlanSubsequentEventTextBlock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap-ebp_EbpSubsequentEventLineItems_019e88c3-c07d-7c54-900a-40af8d7c4166" xlink:to="loc_us-gaap-ebp_EmployeeBenefitPlanSubsequentEventTextBlock_019e88c3-c07d-75b9-b0e7-70a46ed0509b" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.mdu.com/role/ScheduleHLine4iScheduleofAssetsHeldAtEndofYear" xlink:type="simple" xlink:href="mdu-20260618.xsd#ScheduleHLine4iScheduleofAssetsHeldAtEndofYear"/>
  <link:definitionLink xlink:role="http://www.mdu.com/role/ScheduleHLine4iScheduleofAssetsHeldAtEndofYear" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap-ebp_EmployeeBenefitPlanScheduleOfAssetHeldForInvestmentLineItems_019e88c3-c07d-7e20-a1f3-fae3e31d6252" xlink:href="https://xbrl.fasb.org/us-gaap/2026/ebp/elts/us-gaap-ebp-2026.xsd#us-gaap-ebp_EmployeeBenefitPlanScheduleOfAssetHeldForInvestmentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap-ebp_EmployeeBenefitPlanScheduleOfAssetHeldForInvestmentTable_019e88c3-c07d-71c8-ac11-3da0e5230179" xlink:href="https://xbrl.fasb.org/us-gaap/2026/ebp/elts/us-gaap-ebp-2026.xsd#us-gaap-ebp_EmployeeBenefitPlanScheduleOfAssetHeldForInvestmentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap-ebp_EmployeeBenefitPlanScheduleOfAssetHeldForInvestmentLineItems_019e88c3-c07d-7e20-a1f3-fae3e31d6252" xlink:to="loc_us-gaap-ebp_EmployeeBenefitPlanScheduleOfAssetHeldForInvestmentTable_019e88c3-c07d-71c8-ac11-3da0e5230179" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_019e88c3-c07d-79b9-93df-fffca50b137d" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_LegalEntityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap-ebp_EmployeeBenefitPlanScheduleOfAssetHeldForInvestmentTable_019e88c3-c07d-71c8-ac11-3da0e5230179" xlink:to="loc_dei_LegalEntityAxis_019e88c3-c07d-79b9-93df-fffca50b137d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_019e88c3-c07d-79b9-93df-fffca50b137d_default" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_019e88c3-c07d-79b9-93df-fffca50b137d" xlink:to="loc_dei_EntityDomain_019e88c3-c07d-79b9-93df-fffca50b137d_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_019e88c3-c07d-75fb-a438-d0e99de98a86" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_019e88c3-c07d-79b9-93df-fffca50b137d" xlink:to="loc_dei_EntityDomain_019e88c3-c07d-75fb-a438-d0e99de98a86" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_mdu_EBP004Member_019e88c3-c07d-7f2c-8a9e-3171d4881868" xlink:href="mdu-20260618.xsd#mdu_EBP004Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_019e88c3-c07d-75fb-a438-d0e99de98a86" xlink:to="loc_mdu_EBP004Member_019e88c3-c07d-7f2c-8a9e-3171d4881868" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap-ebp_EmployeeBenefitPlanScheduleOfAssetHeldForInvestmentTableTextBlock_019e88c3-c07d-70db-8822-be1d32d09ea4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/ebp/elts/us-gaap-ebp-2026.xsd#us-gaap-ebp_EmployeeBenefitPlanScheduleOfAssetHeldForInvestmentTableTextBlock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap-ebp_EmployeeBenefitPlanScheduleOfAssetHeldForInvestmentLineItems_019e88c3-c07d-7e20-a1f3-fae3e31d6252" xlink:to="loc_us-gaap-ebp_EmployeeBenefitPlanScheduleOfAssetHeldForInvestmentTableTextBlock_019e88c3-c07d-70db-8822-be1d32d09ea4" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.mdu.com/role/SummaryofSignificantAccountingPoliciesPolicies" xlink:type="simple" xlink:href="mdu-20260618.xsd#SummaryofSignificantAccountingPoliciesPolicies"/>
  <link:definitionLink xlink:role="http://www.mdu.com/role/SummaryofSignificantAccountingPoliciesPolicies" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap-ebp_EmployeeBenefitPlanAccountingPolicyLineItems_019e88c3-c07d-7098-8857-837ba30518fe" xlink:href="https://xbrl.fasb.org/us-gaap/2026/ebp/elts/us-gaap-ebp-2026.xsd#us-gaap-ebp_EmployeeBenefitPlanAccountingPolicyLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap-ebp_EmployeeBenefitPlanAccountingPolicyTable_019e88c3-c07d-7699-a89a-7dabfa769e12" xlink:href="https://xbrl.fasb.org/us-gaap/2026/ebp/elts/us-gaap-ebp-2026.xsd#us-gaap-ebp_EmployeeBenefitPlanAccountingPolicyTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap-ebp_EmployeeBenefitPlanAccountingPolicyLineItems_019e88c3-c07d-7098-8857-837ba30518fe" xlink:to="loc_us-gaap-ebp_EmployeeBenefitPlanAccountingPolicyTable_019e88c3-c07d-7699-a89a-7dabfa769e12" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_019e88c3-c07d-79b7-8728-9646bdfad19c" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_LegalEntityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap-ebp_EmployeeBenefitPlanAccountingPolicyTable_019e88c3-c07d-7699-a89a-7dabfa769e12" xlink:to="loc_dei_LegalEntityAxis_019e88c3-c07d-79b7-8728-9646bdfad19c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_019e88c3-c07d-79b7-8728-9646bdfad19c_default" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_019e88c3-c07d-79b7-8728-9646bdfad19c" xlink:to="loc_dei_EntityDomain_019e88c3-c07d-79b7-8728-9646bdfad19c_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_019e88c3-c07d-77bf-8c46-e599ddc2cba0" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_019e88c3-c07d-79b7-8728-9646bdfad19c" xlink:to="loc_dei_EntityDomain_019e88c3-c07d-77bf-8c46-e599ddc2cba0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_mdu_EBP004Member_019e88c3-c07d-7c3e-be01-b1b751f49a52" xlink:href="mdu-20260618.xsd#mdu_EBP004Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_019e88c3-c07d-77bf-8c46-e599ddc2cba0" xlink:to="loc_mdu_EBP004Member_019e88c3-c07d-7c3e-be01-b1b751f49a52" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap-ebp_EmployeeBenefitPlanBasisOfAccountingPolicyTextBlock_019e88c3-c07d-7d72-bbf6-22258a0ca21a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/ebp/elts/us-gaap-ebp-2026.xsd#us-gaap-ebp_EmployeeBenefitPlanBasisOfAccountingPolicyTextBlock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap-ebp_EmployeeBenefitPlanAccountingPolicyLineItems_019e88c3-c07d-7098-8857-837ba30518fe" xlink:to="loc_us-gaap-ebp_EmployeeBenefitPlanBasisOfAccountingPolicyTextBlock_019e88c3-c07d-7d72-bbf6-22258a0ca21a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap-ebp_EmployeeBenefitPlanUseOfEstimatePolicyTextBlock_019e88c3-c07d-74d9-b2f5-45c2e6c439ff" xlink:href="https://xbrl.fasb.org/us-gaap/2026/ebp/elts/us-gaap-ebp-2026.xsd#us-gaap-ebp_EmployeeBenefitPlanUseOfEstimatePolicyTextBlock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap-ebp_EmployeeBenefitPlanAccountingPolicyLineItems_019e88c3-c07d-7098-8857-837ba30518fe" xlink:to="loc_us-gaap-ebp_EmployeeBenefitPlanUseOfEstimatePolicyTextBlock_019e88c3-c07d-74d9-b2f5-45c2e6c439ff" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap-ebp_EmployeeBenefitPlanInvestmentPolicyTextBlock_019e88c3-c07d-703a-9530-0ba599afac76" xlink:href="https://xbrl.fasb.org/us-gaap/2026/ebp/elts/us-gaap-ebp-2026.xsd#us-gaap-ebp_EmployeeBenefitPlanInvestmentPolicyTextBlock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap-ebp_EmployeeBenefitPlanAccountingPolicyLineItems_019e88c3-c07d-7098-8857-837ba30518fe" xlink:to="loc_us-gaap-ebp_EmployeeBenefitPlanInvestmentPolicyTextBlock_019e88c3-c07d-703a-9530-0ba599afac76" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap-ebp_EmployeeBenefitPlanNoteReceivableFromParticipantPolicyTextBlock_019e88c3-c07d-77e0-9cdb-40a60c463103" xlink:href="https://xbrl.fasb.org/us-gaap/2026/ebp/elts/us-gaap-ebp-2026.xsd#us-gaap-ebp_EmployeeBenefitPlanNoteReceivableFromParticipantPolicyTextBlock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap-ebp_EmployeeBenefitPlanAccountingPolicyLineItems_019e88c3-c07d-7098-8857-837ba30518fe" xlink:to="loc_us-gaap-ebp_EmployeeBenefitPlanNoteReceivableFromParticipantPolicyTextBlock_019e88c3-c07d-77e0-9cdb-40a60c463103" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap-ebp_EmployeeBenefitPlanPaymentToParticipantPolicyTextBlock_019e88c3-c07d-7ace-ac2b-549e13a6b25b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/ebp/elts/us-gaap-ebp-2026.xsd#us-gaap-ebp_EmployeeBenefitPlanPaymentToParticipantPolicyTextBlock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap-ebp_EmployeeBenefitPlanAccountingPolicyLineItems_019e88c3-c07d-7098-8857-837ba30518fe" xlink:to="loc_us-gaap-ebp_EmployeeBenefitPlanPaymentToParticipantPolicyTextBlock_019e88c3-c07d-7ace-ac2b-549e13a6b25b" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap-ebp_EmployeeBenefitPlanContributionPolicyTextBlock_019e88c3-c07d-7241-9845-74a602a93af7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/ebp/elts/us-gaap-ebp-2026.xsd#us-gaap-ebp_EmployeeBenefitPlanContributionPolicyTextBlock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap-ebp_EmployeeBenefitPlanAccountingPolicyLineItems_019e88c3-c07d-7098-8857-837ba30518fe" xlink:to="loc_us-gaap-ebp_EmployeeBenefitPlanContributionPolicyTextBlock_019e88c3-c07d-7241-9845-74a602a93af7" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap-ebp_EmployeeBenefitPlanExpensePolicyTextBlock_019e88c3-c07d-79e0-9dbc-9a93930a4b18" xlink:href="https://xbrl.fasb.org/us-gaap/2026/ebp/elts/us-gaap-ebp-2026.xsd#us-gaap-ebp_EmployeeBenefitPlanExpensePolicyTextBlock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap-ebp_EmployeeBenefitPlanAccountingPolicyLineItems_019e88c3-c07d-7098-8857-837ba30518fe" xlink:to="loc_us-gaap-ebp_EmployeeBenefitPlanExpensePolicyTextBlock_019e88c3-c07d-79e0-9dbc-9a93930a4b18" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap-ebp_EbpRiskAndUncertaintyPolicyTextBlock_019e88c3-c07d-75b2-94ac-6e4e00c93ba5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/ebp/elts/us-gaap-ebp-2026.xsd#us-gaap-ebp_EbpRiskAndUncertaintyPolicyTextBlock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap-ebp_EmployeeBenefitPlanAccountingPolicyLineItems_019e88c3-c07d-7098-8857-837ba30518fe" xlink:to="loc_us-gaap-ebp_EbpRiskAndUncertaintyPolicyTextBlock_019e88c3-c07d-75b2-94ac-6e4e00c93ba5" xlink:type="arc" order="7"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.mdu.com/role/SummaryofSignificantAccountingPoliciesTables" xlink:type="simple" xlink:href="mdu-20260618.xsd#SummaryofSignificantAccountingPoliciesTables"/>
  <link:definitionLink xlink:role="http://www.mdu.com/role/SummaryofSignificantAccountingPoliciesTables" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap-ebp_EmployeeBenefitPlanAccountingPolicyLineItems_019eadfd-5e40-7c9a-8b7c-51a6112c93e6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/ebp/elts/us-gaap-ebp-2026.xsd#us-gaap-ebp_EmployeeBenefitPlanAccountingPolicyLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap-ebp_EmployeeBenefitPlanAccountingPolicyTable_019eadfd-5e40-731b-8282-17876bbdbde1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/ebp/elts/us-gaap-ebp-2026.xsd#us-gaap-ebp_EmployeeBenefitPlanAccountingPolicyTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap-ebp_EmployeeBenefitPlanAccountingPolicyLineItems_019eadfd-5e40-7c9a-8b7c-51a6112c93e6" xlink:to="loc_us-gaap-ebp_EmployeeBenefitPlanAccountingPolicyTable_019eadfd-5e40-731b-8282-17876bbdbde1" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_019eadfd-5e40-7110-906c-c5ae631b015a" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_LegalEntityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap-ebp_EmployeeBenefitPlanAccountingPolicyTable_019eadfd-5e40-731b-8282-17876bbdbde1" xlink:to="loc_dei_LegalEntityAxis_019eadfd-5e40-7110-906c-c5ae631b015a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_019eadfd-5e40-7110-906c-c5ae631b015a_default" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_019eadfd-5e40-7110-906c-c5ae631b015a" xlink:to="loc_dei_EntityDomain_019eadfd-5e40-7110-906c-c5ae631b015a_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_019eadfd-5e40-732e-bb72-7532f2e26167" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_019eadfd-5e40-7110-906c-c5ae631b015a" xlink:to="loc_dei_EntityDomain_019eadfd-5e40-732e-bb72-7532f2e26167" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_mdu_EBP004Member_019eadfd-5e40-7500-a051-d59e848b2f00" xlink:href="mdu-20260618.xsd#mdu_EBP004Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_019eadfd-5e40-732e-bb72-7532f2e26167" xlink:to="loc_mdu_EBP004Member_019eadfd-5e40-7500-a051-d59e848b2f00" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap-ebp_EbpRiskAndUncertaintyTableTextBlock_019eadfd-5e40-7d23-afb8-24076b18c4ed" xlink:href="https://xbrl.fasb.org/us-gaap/2026/ebp/elts/us-gaap-ebp-2026.xsd#us-gaap-ebp_EbpRiskAndUncertaintyTableTextBlock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap-ebp_EmployeeBenefitPlanAccountingPolicyLineItems_019eadfd-5e40-7c9a-8b7c-51a6112c93e6" xlink:to="loc_us-gaap-ebp_EbpRiskAndUncertaintyTableTextBlock_019eadfd-5e40-7d23-afb8-24076b18c4ed" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.mdu.com/role/FairValueMeasurementsTables" xlink:type="simple" xlink:href="mdu-20260618.xsd#FairValueMeasurementsTables"/>
  <link:definitionLink xlink:role="http://www.mdu.com/role/FairValueMeasurementsTables" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap-ebp_EmployeeBenefitPlanInvestmentFairValueAndNavLineItems_019e88c3-c07d-791b-b02b-42856ca35f06" xlink:href="https://xbrl.fasb.org/us-gaap/2026/ebp/elts/us-gaap-ebp-2026.xsd#us-gaap-ebp_EmployeeBenefitPlanInvestmentFairValueAndNavLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap-ebp_EmployeeBenefitPlanInvestmentFairValueAndNavTable_019e88c3-c07d-7e38-8d14-2ef9aeeedbe9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/ebp/elts/us-gaap-ebp-2026.xsd#us-gaap-ebp_EmployeeBenefitPlanInvestmentFairValueAndNavTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap-ebp_EmployeeBenefitPlanInvestmentFairValueAndNavLineItems_019e88c3-c07d-791b-b02b-42856ca35f06" xlink:to="loc_us-gaap-ebp_EmployeeBenefitPlanInvestmentFairValueAndNavTable_019e88c3-c07d-7e38-8d14-2ef9aeeedbe9" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_019e88c3-c07d-764a-b14b-f9f892a8c28e" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_LegalEntityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap-ebp_EmployeeBenefitPlanInvestmentFairValueAndNavTable_019e88c3-c07d-7e38-8d14-2ef9aeeedbe9" xlink:to="loc_dei_LegalEntityAxis_019e88c3-c07d-764a-b14b-f9f892a8c28e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_019e88c3-c07d-764a-b14b-f9f892a8c28e_default" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_019e88c3-c07d-764a-b14b-f9f892a8c28e" xlink:to="loc_dei_EntityDomain_019e88c3-c07d-764a-b14b-f9f892a8c28e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_019e88c3-c07d-7ed3-a639-e6ff829f8790" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_019e88c3-c07d-764a-b14b-f9f892a8c28e" xlink:to="loc_dei_EntityDomain_019e88c3-c07d-7ed3-a639-e6ff829f8790" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_mdu_EBP004Member_019e88c3-c07d-7f3a-9110-6d901d65502f" xlink:href="mdu-20260618.xsd#mdu_EBP004Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_019e88c3-c07d-7ed3-a639-e6ff829f8790" xlink:to="loc_mdu_EBP004Member_019e88c3-c07d-7f3a-9110-6d901d65502f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap-ebp_EmployeeBenefitPlanInvestmentFairValueAndNavTableTextBlock_019e88c3-c07d-7828-9cf4-6c90b1610421" xlink:href="https://xbrl.fasb.org/us-gaap/2026/ebp/elts/us-gaap-ebp-2026.xsd#us-gaap-ebp_EmployeeBenefitPlanInvestmentFairValueAndNavTableTextBlock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap-ebp_EmployeeBenefitPlanInvestmentFairValueAndNavLineItems_019e88c3-c07d-791b-b02b-42856ca35f06" xlink:to="loc_us-gaap-ebp_EmployeeBenefitPlanInvestmentFairValueAndNavTableTextBlock_019e88c3-c07d-7828-9cf4-6c90b1610421" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.mdu.com/role/ReconciliationofFinancialStatementstoForm5500Tables" xlink:type="simple" xlink:href="mdu-20260618.xsd#ReconciliationofFinancialStatementstoForm5500Tables"/>
  <link:definitionLink xlink:role="http://www.mdu.com/role/ReconciliationofFinancialStatementstoForm5500Tables" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap-ebp_EmployeeBenefitPlanReconciliationToForm5500LineItems_019e88c3-c07d-7af4-8731-7fa096aa2164" xlink:href="https://xbrl.fasb.org/us-gaap/2026/ebp/elts/us-gaap-ebp-2026.xsd#us-gaap-ebp_EmployeeBenefitPlanReconciliationToForm5500LineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap-ebp_EmployeeBenefitPlanReconciliationToForm5500Table_019e88c3-c07d-7c94-8ca2-99cbae337cd4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/ebp/elts/us-gaap-ebp-2026.xsd#us-gaap-ebp_EmployeeBenefitPlanReconciliationToForm5500Table"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap-ebp_EmployeeBenefitPlanReconciliationToForm5500LineItems_019e88c3-c07d-7af4-8731-7fa096aa2164" xlink:to="loc_us-gaap-ebp_EmployeeBenefitPlanReconciliationToForm5500Table_019e88c3-c07d-7c94-8ca2-99cbae337cd4" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_019e88c3-c07d-7afb-aeba-54042b60275f" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_LegalEntityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap-ebp_EmployeeBenefitPlanReconciliationToForm5500Table_019e88c3-c07d-7c94-8ca2-99cbae337cd4" xlink:to="loc_dei_LegalEntityAxis_019e88c3-c07d-7afb-aeba-54042b60275f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_019e88c3-c07d-7afb-aeba-54042b60275f_default" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_019e88c3-c07d-7afb-aeba-54042b60275f" xlink:to="loc_dei_EntityDomain_019e88c3-c07d-7afb-aeba-54042b60275f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_019e88c3-c07d-70ce-80a6-119efa75b05b" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_019e88c3-c07d-7afb-aeba-54042b60275f" xlink:to="loc_dei_EntityDomain_019e88c3-c07d-70ce-80a6-119efa75b05b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_mdu_EBP004Member_019e88c3-c07d-718f-abdb-7578e5603701" xlink:href="mdu-20260618.xsd#mdu_EBP004Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_019e88c3-c07d-70ce-80a6-119efa75b05b" xlink:to="loc_mdu_EBP004Member_019e88c3-c07d-718f-abdb-7578e5603701" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap-ebp_EmployeeBenefitPlanReconciliationToForm5500TableTextBlock_019e88c3-c07d-7fe3-a363-30a08193614e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/ebp/elts/us-gaap-ebp-2026.xsd#us-gaap-ebp_EmployeeBenefitPlanReconciliationToForm5500TableTextBlock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap-ebp_EmployeeBenefitPlanReconciliationToForm5500LineItems_019e88c3-c07d-7af4-8731-7fa096aa2164" xlink:to="loc_us-gaap-ebp_EmployeeBenefitPlanReconciliationToForm5500TableTextBlock_019e88c3-c07d-7fe3-a363-30a08193614e" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.mdu.com/role/DescriptionofthePlanDetails" xlink:type="simple" xlink:href="mdu-20260618.xsd#DescriptionofthePlanDetails"/>
  <link:definitionLink xlink:role="http://www.mdu.com/role/DescriptionofthePlanDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap-ebp_EmployeeBenefitPlanDescriptionOfPlanLineItems_019e88c3-c07d-7892-bee2-e110b5b5e6de" xlink:href="https://xbrl.fasb.org/us-gaap/2026/ebp/elts/us-gaap-ebp-2026.xsd#us-gaap-ebp_EmployeeBenefitPlanDescriptionOfPlanLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap-ebp_EmployeeBenefitPlanDescriptionOfPlanTable_019e88c3-c07d-7828-92dd-1b0ee0f22500" xlink:href="https://xbrl.fasb.org/us-gaap/2026/ebp/elts/us-gaap-ebp-2026.xsd#us-gaap-ebp_EmployeeBenefitPlanDescriptionOfPlanTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap-ebp_EmployeeBenefitPlanDescriptionOfPlanLineItems_019e88c3-c07d-7892-bee2-e110b5b5e6de" xlink:to="loc_us-gaap-ebp_EmployeeBenefitPlanDescriptionOfPlanTable_019e88c3-c07d-7828-92dd-1b0ee0f22500" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_019e88c3-c07d-7b00-b0a9-021e16ce9572" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_LegalEntityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap-ebp_EmployeeBenefitPlanDescriptionOfPlanTable_019e88c3-c07d-7828-92dd-1b0ee0f22500" xlink:to="loc_dei_LegalEntityAxis_019e88c3-c07d-7b00-b0a9-021e16ce9572" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_019e88c3-c07d-7b00-b0a9-021e16ce9572_default" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_019e88c3-c07d-7b00-b0a9-021e16ce9572" xlink:to="loc_dei_EntityDomain_019e88c3-c07d-7b00-b0a9-021e16ce9572_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_019e88c3-c07d-73c9-a4a4-5dbc149e7aa6" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_019e88c3-c07d-7b00-b0a9-021e16ce9572" xlink:to="loc_dei_EntityDomain_019e88c3-c07d-73c9-a4a4-5dbc149e7aa6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_mdu_EBP004Member_019e88c3-c07d-7bc8-a4d1-88deb5a9685b" xlink:href="mdu-20260618.xsd#mdu_EBP004Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_019e88c3-c07d-73c9-a4a4-5dbc149e7aa6" xlink:to="loc_mdu_EBP004Member_019e88c3-c07d-7bc8-a4d1-88deb5a9685b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_019e8902-5a3a-7654-b82a-15966bd3df4b" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap-ebp_EmployeeBenefitPlanDescriptionOfPlanTable_019e88c3-c07d-7828-92dd-1b0ee0f22500" xlink:to="loc_srt_RangeAxis_019e8902-5a3a-7654-b82a-15966bd3df4b" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_019e8902-5a3a-7654-b82a-15966bd3df4b_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_019e8902-5a3a-7654-b82a-15966bd3df4b" xlink:to="loc_srt_RangeMember_019e8902-5a3a-7654-b82a-15966bd3df4b_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_019e8902-5a3a-7b86-a3e5-4680409a7b1c" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_019e8902-5a3a-7654-b82a-15966bd3df4b" xlink:to="loc_srt_RangeMember_019e8902-5a3a-7b86-a3e5-4680409a7b1c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_019e8902-5a3a-7267-983f-fd7dbcbbd687" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_019e8902-5a3a-7b86-a3e5-4680409a7b1c" xlink:to="loc_srt_MaximumMember_019e8902-5a3a-7267-983f-fd7dbcbbd687" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_019e891f-16de-7942-80b6-a5f4951da2d4" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_019e8902-5a3a-7b86-a3e5-4680409a7b1c" xlink:to="loc_srt_MinimumMember_019e891f-16de-7942-80b6-a5f4951da2d4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_mdu_EBPEmployerContributionTypeAxis_019e8910-e16d-7482-9d10-abf9c59da558" xlink:href="mdu-20260618.xsd#mdu_EBPEmployerContributionTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap-ebp_EmployeeBenefitPlanDescriptionOfPlanTable_019e88c3-c07d-7828-92dd-1b0ee0f22500" xlink:to="loc_mdu_EBPEmployerContributionTypeAxis_019e8910-e16d-7482-9d10-abf9c59da558" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_mdu_EBPEmployerContributionTypeDomain_019e8910-e16d-7482-9d10-abf9c59da558_default" xlink:href="mdu-20260618.xsd#mdu_EBPEmployerContributionTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_mdu_EBPEmployerContributionTypeAxis_019e8910-e16d-7482-9d10-abf9c59da558" xlink:to="loc_mdu_EBPEmployerContributionTypeDomain_019e8910-e16d-7482-9d10-abf9c59da558_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_mdu_EBPEmployerContributionTypeDomain_019e8910-e16d-752b-8e5d-c11c6c898548" xlink:href="mdu-20260618.xsd#mdu_EBPEmployerContributionTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_mdu_EBPEmployerContributionTypeAxis_019e8910-e16d-7482-9d10-abf9c59da558" xlink:to="loc_mdu_EBPEmployerContributionTypeDomain_019e8910-e16d-752b-8e5d-c11c6c898548" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_mdu_EBPDiscretionaryProfitSharingContributionMember_019e8911-1d96-7337-af9e-6dd84be20b19" xlink:href="mdu-20260618.xsd#mdu_EBPDiscretionaryProfitSharingContributionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_mdu_EBPEmployerContributionTypeDomain_019e8910-e16d-752b-8e5d-c11c6c898548" xlink:to="loc_mdu_EBPDiscretionaryProfitSharingContributionMember_019e8911-1d96-7337-af9e-6dd84be20b19" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_mdu_EBPDividendsPaidMember_019e8912-ee9f-7fcb-8137-579623b9acef" xlink:href="mdu-20260618.xsd#mdu_EBPDividendsPaidMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_mdu_EBPEmployerContributionTypeDomain_019e8910-e16d-752b-8e5d-c11c6c898548" xlink:to="loc_mdu_EBPDividendsPaidMember_019e8912-ee9f-7fcb-8137-579623b9acef" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupClassificationAxis_019ed71e-f7e3-79e8-89df-cc55bc218cb4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisposalGroupClassificationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap-ebp_EmployeeBenefitPlanDescriptionOfPlanTable_019e88c3-c07d-7828-92dd-1b0ee0f22500" xlink:to="loc_us-gaap_DisposalGroupClassificationAxis_019ed71e-f7e3-79e8-89df-cc55bc218cb4" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupClassificationDomain_019ed71e-f7e3-79e8-89df-cc55bc218cb4_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisposalGroupClassificationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DisposalGroupClassificationAxis_019ed71e-f7e3-79e8-89df-cc55bc218cb4" xlink:to="loc_us-gaap_DisposalGroupClassificationDomain_019ed71e-f7e3-79e8-89df-cc55bc218cb4_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupClassificationDomain_019ed720-3a6e-7aea-80ea-c0a859caf834" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisposalGroupClassificationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DisposalGroupClassificationAxis_019ed71e-f7e3-79e8-89df-cc55bc218cb4" xlink:to="loc_us-gaap_DisposalGroupClassificationDomain_019ed720-3a6e-7aea-80ea-c0a859caf834" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DiscontinuedOperationsDisposedOfByMeansOtherThanSaleSpinoffMember_019ed71f-0670-7bf0-be91-53c8d5c62051" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DiscontinuedOperationsDisposedOfByMeansOtherThanSaleSpinoffMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisposalGroupClassificationDomain_019ed720-3a6e-7aea-80ea-c0a859caf834" xlink:to="loc_us-gaap_DiscontinuedOperationsDisposedOfByMeansOtherThanSaleSpinoffMember_019ed71f-0670-7bf0-be91-53c8d5c62051" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_019ed71f-3251-71d2-9326-8d4c77ee2504" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap-ebp_EmployeeBenefitPlanDescriptionOfPlanTable_019e88c3-c07d-7828-92dd-1b0ee0f22500" xlink:to="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_019ed71f-3251-71d2-9326-8d4c77ee2504" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_019ed71f-3251-71d2-9326-8d4c77ee2504_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_019ed71f-3251-71d2-9326-8d4c77ee2504" xlink:to="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_019ed71f-3251-71d2-9326-8d4c77ee2504_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_019ed720-70f4-7a38-b999-acdc802d8475" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_019ed71f-3251-71d2-9326-8d4c77ee2504" xlink:to="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_019ed720-70f4-7a38-b999-acdc802d8475" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_mdu_EverusMember_019ed71f-687e-7190-90e9-49ee8ae93ae4" xlink:href="mdu-20260618.xsd#mdu_EverusMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_019ed720-70f4-7a38-b999-acdc802d8475" xlink:to="loc_mdu_EverusMember_019ed71f-687e-7190-90e9-49ee8ae93ae4" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap-ebp_EmployeeBenefitPlanChangeInNetAssetAvailableForBenefitTransferToFromExternalPlan_019eada7-b5ce-7bf0-9d80-b5cdfd0f5e80" xlink:href="https://xbrl.fasb.org/us-gaap/2026/ebp/elts/us-gaap-ebp-2026.xsd#us-gaap-ebp_EmployeeBenefitPlanChangeInNetAssetAvailableForBenefitTransferToFromExternalPlan"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap-ebp_EmployeeBenefitPlanDescriptionOfPlanLineItems_019e88c3-c07d-7892-bee2-e110b5b5e6de" xlink:to="loc_us-gaap-ebp_EmployeeBenefitPlanChangeInNetAssetAvailableForBenefitTransferToFromExternalPlan_019eada7-b5ce-7bf0-9d80-b5cdfd0f5e80" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_mdu_EBPMinimumAgeOfParticipant_019e88e4-5f48-75bb-9bfe-21816694f7ff" xlink:href="mdu-20260618.xsd#mdu_EBPMinimumAgeOfParticipant"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap-ebp_EmployeeBenefitPlanDescriptionOfPlanLineItems_019e88c3-c07d-7892-bee2-e110b5b5e6de" xlink:to="loc_mdu_EBPMinimumAgeOfParticipant_019e88e4-5f48-75bb-9bfe-21816694f7ff" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_mdu_EBPParticipantContributionMaximumContributionToEligibleCompensationPercentage_019e88e7-6bce-7373-be43-559425a79af5" xlink:href="mdu-20260618.xsd#mdu_EBPParticipantContributionMaximumContributionToEligibleCompensationPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap-ebp_EmployeeBenefitPlanDescriptionOfPlanLineItems_019e88c3-c07d-7892-bee2-e110b5b5e6de" xlink:to="loc_mdu_EBPParticipantContributionMaximumContributionToEligibleCompensationPercentage_019e88e7-6bce-7373-be43-559425a79af5" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_mdu_EBPParticipantContributionAutomaticAnnualIncreaseDeferralRate_019e8900-d588-77d5-9ab9-78afa1c174ec" xlink:href="mdu-20260618.xsd#mdu_EBPParticipantContributionAutomaticAnnualIncreaseDeferralRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap-ebp_EmployeeBenefitPlanDescriptionOfPlanLineItems_019e88c3-c07d-7892-bee2-e110b5b5e6de" xlink:to="loc_mdu_EBPParticipantContributionAutomaticAnnualIncreaseDeferralRate_019e8900-d588-77d5-9ab9-78afa1c174ec" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap-ebp_EmployeeBenefitPlanParticipantContributionAutomaticDeferralRate_019e8902-5a3a-7029-a8ac-4225ac5ba3d6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/ebp/elts/us-gaap-ebp-2026.xsd#us-gaap-ebp_EmployeeBenefitPlanParticipantContributionAutomaticDeferralRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap-ebp_EmployeeBenefitPlanDescriptionOfPlanLineItems_019e88c3-c07d-7892-bee2-e110b5b5e6de" xlink:to="loc_us-gaap-ebp_EmployeeBenefitPlanParticipantContributionAutomaticDeferralRate_019e8902-5a3a-7029-a8ac-4225ac5ba3d6" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_mdu_EBPEmployerContributionAmountCreditedToParticipantAccounts_019ea7ae-1b2c-7852-a00e-0c7048681ea5" xlink:href="mdu-20260618.xsd#mdu_EBPEmployerContributionAmountCreditedToParticipantAccounts"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap-ebp_EmployeeBenefitPlanDescriptionOfPlanLineItems_019e88c3-c07d-7892-bee2-e110b5b5e6de" xlink:to="loc_mdu_EBPEmployerContributionAmountCreditedToParticipantAccounts_019ea7ae-1b2c-7852-a00e-0c7048681ea5" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_mdu_EBPEmployerContributionAmountCreditedToParticipantAccountsAccruedButNotPaid_019ea7b0-6413-766e-b2fe-52cec42a0b92" xlink:href="mdu-20260618.xsd#mdu_EBPEmployerContributionAmountCreditedToParticipantAccountsAccruedButNotPaid"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap-ebp_EmployeeBenefitPlanDescriptionOfPlanLineItems_019e88c3-c07d-7892-bee2-e110b5b5e6de" xlink:to="loc_mdu_EBPEmployerContributionAmountCreditedToParticipantAccountsAccruedButNotPaid_019ea7b0-6413-766e-b2fe-52cec42a0b92" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_mdu_EBPInvestmentElectedContributionPercentageIncrement_019ed72d-a6d6-71be-b6fe-fb3ae7d12977" xlink:href="mdu-20260618.xsd#mdu_EBPInvestmentElectedContributionPercentageIncrement"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap-ebp_EmployeeBenefitPlanDescriptionOfPlanLineItems_019e88c3-c07d-7892-bee2-e110b5b5e6de" xlink:to="loc_mdu_EBPInvestmentElectedContributionPercentageIncrement_019ed72d-a6d6-71be-b6fe-fb3ae7d12977" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_mdu_EBPEmployerContributionVestingPercentage_019e8910-e16d-7669-934d-4364eaba44e3" xlink:href="mdu-20260618.xsd#mdu_EBPEmployerContributionVestingPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap-ebp_EmployeeBenefitPlanDescriptionOfPlanLineItems_019e88c3-c07d-7892-bee2-e110b5b5e6de" xlink:to="loc_mdu_EBPEmployerContributionVestingPercentage_019e8910-e16d-7669-934d-4364eaba44e3" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_mdu_EBPEmployerContributionVestingServicePeriod_019e8912-062a-7d3e-8ee3-d3215f2d7c65" xlink:href="mdu-20260618.xsd#mdu_EBPEmployerContributionVestingServicePeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap-ebp_EmployeeBenefitPlanDescriptionOfPlanLineItems_019e88c3-c07d-7892-bee2-e110b5b5e6de" xlink:to="loc_mdu_EBPEmployerContributionVestingServicePeriod_019e8912-062a-7d3e-8ee3-d3215f2d7c65" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_mdu_EBPDistributionsToParticipantsFlexibleInstallmentsPeriodMaximum_019eb238-9003-7255-92ce-8dc921401825" xlink:href="mdu-20260618.xsd#mdu_EBPDistributionsToParticipantsFlexibleInstallmentsPeriodMaximum"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap-ebp_EmployeeBenefitPlanDescriptionOfPlanLineItems_019e88c3-c07d-7892-bee2-e110b5b5e6de" xlink:to="loc_mdu_EBPDistributionsToParticipantsFlexibleInstallmentsPeriodMaximum_019eb238-9003-7255-92ce-8dc921401825" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_mdu_EBPDistributionsToParticipantsRequestedPriorToYearEndButNotPaid_019ea7b9-207a-7e2c-82cc-71c1cffc1385" xlink:href="mdu-20260618.xsd#mdu_EBPDistributionsToParticipantsRequestedPriorToYearEndButNotPaid"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap-ebp_EmployeeBenefitPlanDescriptionOfPlanLineItems_019e88c3-c07d-7892-bee2-e110b5b5e6de" xlink:to="loc_mdu_EBPDistributionsToParticipantsRequestedPriorToYearEndButNotPaid_019ea7b9-207a-7e2c-82cc-71c1cffc1385" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap-ebp_EmployeeBenefitPlanNoteReceivableFromParticipantAccountMinimumBorrowingAmount_019e891c-8f65-7205-801b-814414f015ad" xlink:href="https://xbrl.fasb.org/us-gaap/2026/ebp/elts/us-gaap-ebp-2026.xsd#us-gaap-ebp_EmployeeBenefitPlanNoteReceivableFromParticipantAccountMinimumBorrowingAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap-ebp_EmployeeBenefitPlanDescriptionOfPlanLineItems_019e88c3-c07d-7892-bee2-e110b5b5e6de" xlink:to="loc_us-gaap-ebp_EmployeeBenefitPlanNoteReceivableFromParticipantAccountMinimumBorrowingAmount_019e891c-8f65-7205-801b-814414f015ad" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap-ebp_EmployeeBenefitPlanNoteReceivableFromParticipantAccountMaximumBorrowingAmount_019e891c-ffce-753b-a5c5-dfbef88dd5dc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/ebp/elts/us-gaap-ebp-2026.xsd#us-gaap-ebp_EmployeeBenefitPlanNoteReceivableFromParticipantAccountMaximumBorrowingAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap-ebp_EmployeeBenefitPlanDescriptionOfPlanLineItems_019e88c3-c07d-7892-bee2-e110b5b5e6de" xlink:to="loc_us-gaap-ebp_EmployeeBenefitPlanNoteReceivableFromParticipantAccountMaximumBorrowingAmount_019e891c-ffce-753b-a5c5-dfbef88dd5dc" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap-ebp_EmployeeBenefitPlanNoteReceivableFromParticipantAccountMaximumBorrowingToTotalAccountPercentage_019e891e-09df-70a9-8ad0-bd334202d4aa" xlink:href="https://xbrl.fasb.org/us-gaap/2026/ebp/elts/us-gaap-ebp-2026.xsd#us-gaap-ebp_EmployeeBenefitPlanNoteReceivableFromParticipantAccountMaximumBorrowingToTotalAccountPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap-ebp_EmployeeBenefitPlanDescriptionOfPlanLineItems_019e88c3-c07d-7892-bee2-e110b5b5e6de" xlink:to="loc_us-gaap-ebp_EmployeeBenefitPlanNoteReceivableFromParticipantAccountMaximumBorrowingToTotalAccountPercentage_019e891e-09df-70a9-8ad0-bd334202d4aa" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_mdu_EBPDisposalGroupIncludingDiscontinuedOperationStockSplitConversionRatio_019ed71e-9b79-7ff6-b9c2-455b35f0cb8c" xlink:href="mdu-20260618.xsd#mdu_EBPDisposalGroupIncludingDiscontinuedOperationStockSplitConversionRatio"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap-ebp_EmployeeBenefitPlanDescriptionOfPlanLineItems_019e88c3-c07d-7892-bee2-e110b5b5e6de" xlink:to="loc_mdu_EBPDisposalGroupIncludingDiscontinuedOperationStockSplitConversionRatio_019ed71e-9b79-7ff6-b9c2-455b35f0cb8c" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap-ebp_EmployeeBenefitPlanParticipantLoanInterestRate_019e891f-46c1-73ad-b5db-e93891b04570" xlink:href="https://xbrl.fasb.org/us-gaap/2026/ebp/elts/us-gaap-ebp-2026.xsd#us-gaap-ebp_EmployeeBenefitPlanParticipantLoanInterestRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap-ebp_EmployeeBenefitPlanDescriptionOfPlanLineItems_019e88c3-c07d-7892-bee2-e110b5b5e6de" xlink:to="loc_us-gaap-ebp_EmployeeBenefitPlanParticipantLoanInterestRate_019e891f-46c1-73ad-b5db-e93891b04570" xlink:type="arc" order="16"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap-ebp_EmployeeBenefitPlanForfeitedNonvestedAccount_019e8922-b93b-725c-a540-f5637e99ef35" xlink:href="https://xbrl.fasb.org/us-gaap/2026/ebp/elts/us-gaap-ebp-2026.xsd#us-gaap-ebp_EmployeeBenefitPlanForfeitedNonvestedAccount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap-ebp_EmployeeBenefitPlanDescriptionOfPlanLineItems_019e88c3-c07d-7892-bee2-e110b5b5e6de" xlink:to="loc_us-gaap-ebp_EmployeeBenefitPlanForfeitedNonvestedAccount_019e8922-b93b-725c-a540-f5637e99ef35" xlink:type="arc" order="17"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap-ebp_EmployeeBenefitPlanForfeitedNonvestedAccountDecreaseForEmployerContribution_019e8923-e9c5-7c78-9892-09273d97eee7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/ebp/elts/us-gaap-ebp-2026.xsd#us-gaap-ebp_EmployeeBenefitPlanForfeitedNonvestedAccountDecreaseForEmployerContribution"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap-ebp_EmployeeBenefitPlanDescriptionOfPlanLineItems_019e88c3-c07d-7892-bee2-e110b5b5e6de" xlink:to="loc_us-gaap-ebp_EmployeeBenefitPlanForfeitedNonvestedAccountDecreaseForEmployerContribution_019e8923-e9c5-7c78-9892-09273d97eee7" xlink:type="arc" order="18"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.mdu.com/role/SummaryofAccountingPoliciesDetails" xlink:type="simple" xlink:href="mdu-20260618.xsd#SummaryofAccountingPoliciesDetails"/>
  <link:definitionLink xlink:role="http://www.mdu.com/role/SummaryofAccountingPoliciesDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap-ebp_EmployeeBenefitPlanAccountingPolicyLineItems_019e88c3-c07d-70be-ad12-cf0d794d5001" xlink:href="https://xbrl.fasb.org/us-gaap/2026/ebp/elts/us-gaap-ebp-2026.xsd#us-gaap-ebp_EmployeeBenefitPlanAccountingPolicyLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap-ebp_EmployeeBenefitPlanAccountingPolicyTable_019e88c3-c07d-70d9-ac46-8a92ec60ea82" xlink:href="https://xbrl.fasb.org/us-gaap/2026/ebp/elts/us-gaap-ebp-2026.xsd#us-gaap-ebp_EmployeeBenefitPlanAccountingPolicyTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap-ebp_EmployeeBenefitPlanAccountingPolicyLineItems_019e88c3-c07d-70be-ad12-cf0d794d5001" xlink:to="loc_us-gaap-ebp_EmployeeBenefitPlanAccountingPolicyTable_019e88c3-c07d-70d9-ac46-8a92ec60ea82" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_019ea83a-4a9c-729a-b3af-6627a3465eaa" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_LegalEntityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap-ebp_EmployeeBenefitPlanAccountingPolicyTable_019e88c3-c07d-70d9-ac46-8a92ec60ea82" xlink:to="loc_dei_LegalEntityAxis_019ea83a-4a9c-729a-b3af-6627a3465eaa" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_019ea83a-4a9c-729a-b3af-6627a3465eaa_default" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_019ea83a-4a9c-729a-b3af-6627a3465eaa" xlink:to="loc_dei_EntityDomain_019ea83a-4a9c-729a-b3af-6627a3465eaa_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_019ea83a-4a9c-7afe-a6c9-3dfc6213aa09" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_019ea83a-4a9c-729a-b3af-6627a3465eaa" xlink:to="loc_dei_EntityDomain_019ea83a-4a9c-7afe-a6c9-3dfc6213aa09" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_mdu_EBP004Member_019ea83a-4a9c-7c1d-bec9-e5c0fd7cd52b" xlink:href="mdu-20260618.xsd#mdu_EBP004Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_019ea83a-4a9c-7afe-a6c9-3dfc6213aa09" xlink:to="loc_mdu_EBP004Member_019ea83a-4a9c-7c1d-bec9-e5c0fd7cd52b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap-ebp_EmployeeBenefitPlanChangeInNetAssetAvailableForBenefitDecreaseForAdministrativeExpense_019e8927-6f27-7eea-8fab-b489e43db972" xlink:href="https://xbrl.fasb.org/us-gaap/2026/ebp/elts/us-gaap-ebp-2026.xsd#us-gaap-ebp_EmployeeBenefitPlanChangeInNetAssetAvailableForBenefitDecreaseForAdministrativeExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap-ebp_EmployeeBenefitPlanAccountingPolicyLineItems_019e88c3-c07d-70be-ad12-cf0d794d5001" xlink:to="loc_us-gaap-ebp_EmployeeBenefitPlanChangeInNetAssetAvailableForBenefitDecreaseForAdministrativeExpense_019e8927-6f27-7eea-8fab-b489e43db972" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_mdu_EBPFeesAndCommissionsAssociatedWithInvestmentsOtherThanCommonStock_019e88c3-c07d-77c2-a9fe-fff8e25e6ea4" xlink:href="mdu-20260618.xsd#mdu_EBPFeesAndCommissionsAssociatedWithInvestmentsOtherThanCommonStock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap-ebp_EmployeeBenefitPlanAccountingPolicyLineItems_019e88c3-c07d-70be-ad12-cf0d794d5001" xlink:to="loc_mdu_EBPFeesAndCommissionsAssociatedWithInvestmentsOtherThanCommonStock_019e88c3-c07d-77c2-a9fe-fff8e25e6ea4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_mdu_EBPRevenueSharingAdjustmentFeeLevelization_019e8928-7bea-71ce-9752-75b0733397dc" xlink:href="mdu-20260618.xsd#mdu_EBPRevenueSharingAdjustmentFeeLevelization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap-ebp_EmployeeBenefitPlanAccountingPolicyLineItems_019e88c3-c07d-70be-ad12-cf0d794d5001" xlink:to="loc_mdu_EBPRevenueSharingAdjustmentFeeLevelization_019e8928-7bea-71ce-9752-75b0733397dc" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.mdu.com/role/SummaryofSignificantAccountingPoliciesSummaryofConcentrationofInvestmentsDetails" xlink:type="simple" xlink:href="mdu-20260618.xsd#SummaryofSignificantAccountingPoliciesSummaryofConcentrationofInvestmentsDetails"/>
  <link:definitionLink xlink:role="http://www.mdu.com/role/SummaryofSignificantAccountingPoliciesSummaryofConcentrationofInvestmentsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap-ebp_EbpAccountingStandardUpdateAndChangeInAccountingPrincipleLineItems_019e8929-a006-72c6-9f42-7e4c0713596e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/ebp/elts/us-gaap-ebp-2026.xsd#us-gaap-ebp_EbpAccountingStandardUpdateAndChangeInAccountingPrincipleLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap-ebp_EbpAccountingStandardUpdateAndChangeInAccountingPrincipleTable_019e8929-a006-7fa1-93f2-ba206a21bb97" xlink:href="https://xbrl.fasb.org/us-gaap/2026/ebp/elts/us-gaap-ebp-2026.xsd#us-gaap-ebp_EbpAccountingStandardUpdateAndChangeInAccountingPrincipleTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap-ebp_EbpAccountingStandardUpdateAndChangeInAccountingPrincipleLineItems_019e8929-a006-72c6-9f42-7e4c0713596e" xlink:to="loc_us-gaap-ebp_EbpAccountingStandardUpdateAndChangeInAccountingPrincipleTable_019e8929-a006-7fa1-93f2-ba206a21bb97" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentTypeAxis_019e8929-a006-7e3b-918d-96b9f5c146de" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InvestmentTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap-ebp_EbpAccountingStandardUpdateAndChangeInAccountingPrincipleTable_019e8929-a006-7fa1-93f2-ba206a21bb97" xlink:to="loc_us-gaap_InvestmentTypeAxis_019e8929-a006-7e3b-918d-96b9f5c146de" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentTypeCategorizationMember_019e8929-a006-7e3b-918d-96b9f5c146de_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InvestmentTypeCategorizationMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_InvestmentTypeAxis_019e8929-a006-7e3b-918d-96b9f5c146de" xlink:to="loc_us-gaap_InvestmentTypeCategorizationMember_019e8929-a006-7e3b-918d-96b9f5c146de_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentTypeCategorizationMember_019e8929-a006-77b5-b1b7-1fd047bcd399" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InvestmentTypeCategorizationMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_InvestmentTypeAxis_019e8929-a006-7e3b-918d-96b9f5c146de" xlink:to="loc_us-gaap_InvestmentTypeCategorizationMember_019e8929-a006-77b5-b1b7-1fd047bcd399" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_mdu_EBPFidelity500IndexFundMember_019ea7bc-d81b-7f26-8309-40cd9b1f6d03" xlink:href="mdu-20260618.xsd#mdu_EBPFidelity500IndexFundMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InvestmentTypeCategorizationMember_019e8929-a006-77b5-b1b7-1fd047bcd399" xlink:to="loc_mdu_EBPFidelity500IndexFundMember_019ea7bc-d81b-7f26-8309-40cd9b1f6d03" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap-ebp_EmployeeBenefitPlanEmployerCommonStockMember_019e8929-a006-70ba-ae64-5ed26a968ba5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/ebp/elts/us-gaap-ebp-2026.xsd#us-gaap-ebp_EmployeeBenefitPlanEmployerCommonStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InvestmentTypeCategorizationMember_019e8929-a006-77b5-b1b7-1fd047bcd399" xlink:to="loc_us-gaap-ebp_EmployeeBenefitPlanEmployerCommonStockMember_019e8929-a006-70ba-ae64-5ed26a968ba5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_mdu_EBPTRowePriceLargeCapGrowthFundMember_019ea7be-6fc4-7807-819d-e4ee3304e0d3" xlink:href="mdu-20260618.xsd#mdu_EBPTRowePriceLargeCapGrowthFundMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InvestmentTypeCategorizationMember_019e8929-a006-77b5-b1b7-1fd047bcd399" xlink:to="loc_mdu_EBPTRowePriceLargeCapGrowthFundMember_019ea7be-6fc4-7807-819d-e4ee3304e0d3" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_mdu_EBPVanguardInstitutionalIndexFundMember_019ea7d6-6987-7d48-af6c-4a44d11ff950" xlink:href="mdu-20260618.xsd#mdu_EBPVanguardInstitutionalIndexFundMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InvestmentTypeCategorizationMember_019e8929-a006-77b5-b1b7-1fd047bcd399" xlink:to="loc_mdu_EBPVanguardInstitutionalIndexFundMember_019ea7d6-6987-7d48-af6c-4a44d11ff950" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_019e8929-a006-7ba6-8afd-c90887217add" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_LegalEntityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap-ebp_EbpAccountingStandardUpdateAndChangeInAccountingPrincipleTable_019e8929-a006-7fa1-93f2-ba206a21bb97" xlink:to="loc_dei_LegalEntityAxis_019e8929-a006-7ba6-8afd-c90887217add" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_019e8929-a006-7ba6-8afd-c90887217add_default" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_019e8929-a006-7ba6-8afd-c90887217add" xlink:to="loc_dei_EntityDomain_019e8929-a006-7ba6-8afd-c90887217add_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_019e8929-a006-722c-bc7c-04606df5f421" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_019e8929-a006-7ba6-8afd-c90887217add" xlink:to="loc_dei_EntityDomain_019e8929-a006-722c-bc7c-04606df5f421" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_mdu_EBP004Member_019e8929-a006-7f4b-b108-02ff2317d1b3" xlink:href="mdu-20260618.xsd#mdu_EBP004Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_019e8929-a006-722c-bc7c-04606df5f421" xlink:to="loc_mdu_EBP004Member_019e8929-a006-7f4b-b108-02ff2317d1b3" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap-ebp_EbpRiskAndUncertaintyConcentrationOfInvestmentAtFairValueToNetAssetsAmount_019eb24e-0e68-7fed-81cb-780e45ecd80f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/ebp/elts/us-gaap-ebp-2026.xsd#us-gaap-ebp_EbpRiskAndUncertaintyConcentrationOfInvestmentAtFairValueToNetAssetsAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap-ebp_EbpAccountingStandardUpdateAndChangeInAccountingPrincipleLineItems_019e8929-a006-72c6-9f42-7e4c0713596e" xlink:to="loc_us-gaap-ebp_EbpRiskAndUncertaintyConcentrationOfInvestmentAtFairValueToNetAssetsAmount_019eb24e-0e68-7fed-81cb-780e45ecd80f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap-ebp_EbpRiskAndUncertaintyConcentrationOfInvestmentAtFairValueToNetAssetsPercentage_019eb24e-b40b-7a52-ae1c-d3fde200732d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/ebp/elts/us-gaap-ebp-2026.xsd#us-gaap-ebp_EbpRiskAndUncertaintyConcentrationOfInvestmentAtFairValueToNetAssetsPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap-ebp_EbpAccountingStandardUpdateAndChangeInAccountingPrincipleLineItems_019e8929-a006-72c6-9f42-7e4c0713596e" xlink:to="loc_us-gaap-ebp_EbpRiskAndUncertaintyConcentrationOfInvestmentAtFairValueToNetAssetsPercentage_019eb24e-b40b-7a52-ae1c-d3fde200732d" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.mdu.com/role/InvestmentContractwithInsuranceCompanyDetails" xlink:type="simple" xlink:href="mdu-20260618.xsd#InvestmentContractwithInsuranceCompanyDetails"/>
  <link:definitionLink xlink:role="http://www.mdu.com/role/InvestmentContractwithInsuranceCompanyDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap-ebp_EmployeeBenefitPlanFullyBenefitResponsiveInvestmentContractLineItems_019e88c3-c07d-7229-9bd2-7676763e5f54" xlink:href="https://xbrl.fasb.org/us-gaap/2026/ebp/elts/us-gaap-ebp-2026.xsd#us-gaap-ebp_EmployeeBenefitPlanFullyBenefitResponsiveInvestmentContractLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap-ebp_EmployeeBenefitPlanFullyBenefitResponsiveInvestmentContractTable_019e88c3-c07d-7c07-bf94-52af1dd292ea" xlink:href="https://xbrl.fasb.org/us-gaap/2026/ebp/elts/us-gaap-ebp-2026.xsd#us-gaap-ebp_EmployeeBenefitPlanFullyBenefitResponsiveInvestmentContractTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap-ebp_EmployeeBenefitPlanFullyBenefitResponsiveInvestmentContractLineItems_019e88c3-c07d-7229-9bd2-7676763e5f54" xlink:to="loc_us-gaap-ebp_EmployeeBenefitPlanFullyBenefitResponsiveInvestmentContractTable_019e88c3-c07d-7c07-bf94-52af1dd292ea" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_019e88c3-c07d-7d63-9c9a-4ec9ebd96716" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_LegalEntityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap-ebp_EmployeeBenefitPlanFullyBenefitResponsiveInvestmentContractTable_019e88c3-c07d-7c07-bf94-52af1dd292ea" xlink:to="loc_dei_LegalEntityAxis_019e88c3-c07d-7d63-9c9a-4ec9ebd96716" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_019e88c3-c07d-7d63-9c9a-4ec9ebd96716_default" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_019e88c3-c07d-7d63-9c9a-4ec9ebd96716" xlink:to="loc_dei_EntityDomain_019e88c3-c07d-7d63-9c9a-4ec9ebd96716_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_019e88c3-c07d-7172-b0e0-4b9fc49f8db4" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_019e88c3-c07d-7d63-9c9a-4ec9ebd96716" xlink:to="loc_dei_EntityDomain_019e88c3-c07d-7172-b0e0-4b9fc49f8db4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_mdu_EBP004Member_019e88c3-c07d-71e7-bc7e-38d88af20a94" xlink:href="mdu-20260618.xsd#mdu_EBP004Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_019e88c3-c07d-7172-b0e0-4b9fc49f8db4" xlink:to="loc_mdu_EBP004Member_019e88c3-c07d-71e7-bc7e-38d88af20a94" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap-ebp_EmployeeBenefitPlanInvestmentExcludingPlanInterestInMasterTrustContractValue_019eade9-351f-76e5-9510-b32e0e7fe958" xlink:href="https://xbrl.fasb.org/us-gaap/2026/ebp/elts/us-gaap-ebp-2026.xsd#us-gaap-ebp_EmployeeBenefitPlanInvestmentExcludingPlanInterestInMasterTrustContractValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap-ebp_EmployeeBenefitPlanFullyBenefitResponsiveInvestmentContractLineItems_019e88c3-c07d-7229-9bd2-7676763e5f54" xlink:to="loc_us-gaap-ebp_EmployeeBenefitPlanInvestmentExcludingPlanInterestInMasterTrustContractValue_019eade9-351f-76e5-9510-b32e0e7fe958" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.mdu.com/role/FairValueMeasurementsDetails" xlink:type="simple" xlink:href="mdu-20260618.xsd#FairValueMeasurementsDetails"/>
  <link:definitionLink xlink:role="http://www.mdu.com/role/FairValueMeasurementsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap-ebp_EmployeeBenefitPlanInvestmentFairValueAndNavLineItems_019e88c3-c07d-735b-b623-49a37d5e009c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/ebp/elts/us-gaap-ebp-2026.xsd#us-gaap-ebp_EmployeeBenefitPlanInvestmentFairValueAndNavLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap-ebp_EmployeeBenefitPlanInvestmentFairValueAndNavTable_019e88c3-c07d-7a44-aae1-f665d3936f60" xlink:href="https://xbrl.fasb.org/us-gaap/2026/ebp/elts/us-gaap-ebp-2026.xsd#us-gaap-ebp_EmployeeBenefitPlanInvestmentFairValueAndNavTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap-ebp_EmployeeBenefitPlanInvestmentFairValueAndNavLineItems_019e88c3-c07d-735b-b623-49a37d5e009c" xlink:to="loc_us-gaap-ebp_EmployeeBenefitPlanInvestmentFairValueAndNavTable_019e88c3-c07d-7a44-aae1-f665d3936f60" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_019e88c3-c07d-71ba-9596-5d28047b14b4" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_LegalEntityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap-ebp_EmployeeBenefitPlanInvestmentFairValueAndNavTable_019e88c3-c07d-7a44-aae1-f665d3936f60" xlink:to="loc_dei_LegalEntityAxis_019e88c3-c07d-71ba-9596-5d28047b14b4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_019e88c3-c07d-71ba-9596-5d28047b14b4_default" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_019e88c3-c07d-71ba-9596-5d28047b14b4" xlink:to="loc_dei_EntityDomain_019e88c3-c07d-71ba-9596-5d28047b14b4_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_019e88c3-c07d-7e2c-91b7-18269088722a" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_019e88c3-c07d-71ba-9596-5d28047b14b4" xlink:to="loc_dei_EntityDomain_019e88c3-c07d-7e2c-91b7-18269088722a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_mdu_EBP004Member_019e88c3-c07d-75f1-a079-d2ecbe7161ed" xlink:href="mdu-20260618.xsd#mdu_EBP004Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_019e88c3-c07d-7e2c-91b7-18269088722a" xlink:to="loc_mdu_EBP004Member_019e88c3-c07d-75f1-a079-d2ecbe7161ed" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019e88c3-c07d-72a5-939b-cb29a9e60dac" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap-ebp_EmployeeBenefitPlanInvestmentFairValueAndNavTable_019e88c3-c07d-7a44-aae1-f665d3936f60" xlink:to="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019e88c3-c07d-72a5-939b-cb29a9e60dac" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019e88c3-c07d-72a5-939b-cb29a9e60dac_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019e88c3-c07d-72a5-939b-cb29a9e60dac" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019e88c3-c07d-72a5-939b-cb29a9e60dac_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019e88c3-c07d-7010-b91a-0797b68e324f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019e88c3-c07d-72a5-939b-cb29a9e60dac" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019e88c3-c07d-7010-b91a-0797b68e324f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel12And3Member_019e88c3-c07d-76d8-9095-f6721e507a49" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueInputsLevel12And3Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019e88c3-c07d-7010-b91a-0797b68e324f" xlink:to="loc_us-gaap_FairValueInputsLevel12And3Member_019e88c3-c07d-76d8-9095-f6721e507a49" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel1Member_019e88c3-c07d-72ee-8dd5-11614880bb0c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueInputsLevel1Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueInputsLevel12And3Member_019e88c3-c07d-76d8-9095-f6721e507a49" xlink:to="loc_us-gaap_FairValueInputsLevel1Member_019e88c3-c07d-72ee-8dd5-11614880bb0c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel2Member_019e88c3-c07d-7772-9f1e-faa0089e9811" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueInputsLevel2Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueInputsLevel12And3Member_019e88c3-c07d-76d8-9095-f6721e507a49" xlink:to="loc_us-gaap_FairValueInputsLevel2Member_019e88c3-c07d-7772-9f1e-faa0089e9811" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel3Member_019e88c3-c07d-7963-b755-b309d95e0eab" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueInputsLevel3Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueInputsLevel12And3Member_019e88c3-c07d-76d8-9095-f6721e507a49" xlink:to="loc_us-gaap_FairValueInputsLevel3Member_019e88c3-c07d-7963-b755-b309d95e0eab" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasuredAtNetAssetValuePerShareMember_019ea84f-3c94-7b2d-8315-9a674cf9df8d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueMeasuredAtNetAssetValuePerShareMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019e88c3-c07d-7010-b91a-0797b68e324f" xlink:to="loc_us-gaap_FairValueMeasuredAtNetAssetValuePerShareMember_019ea84f-3c94-7b2d-8315-9a674cf9df8d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentTypeAxis_019e88c3-c07d-742a-887b-16c7299d1297" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InvestmentTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap-ebp_EmployeeBenefitPlanInvestmentFairValueAndNavTable_019e88c3-c07d-7a44-aae1-f665d3936f60" xlink:to="loc_us-gaap_InvestmentTypeAxis_019e88c3-c07d-742a-887b-16c7299d1297" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentTypeCategorizationMember_019e88c3-c07d-742a-887b-16c7299d1297_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InvestmentTypeCategorizationMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_InvestmentTypeAxis_019e88c3-c07d-742a-887b-16c7299d1297" xlink:to="loc_us-gaap_InvestmentTypeCategorizationMember_019e88c3-c07d-742a-887b-16c7299d1297_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentTypeCategorizationMember_019e88c3-c07d-723e-9974-f3f52e236cde" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InvestmentTypeCategorizationMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_InvestmentTypeAxis_019e88c3-c07d-742a-887b-16c7299d1297" xlink:to="loc_us-gaap_InvestmentTypeCategorizationMember_019e88c3-c07d-723e-9974-f3f52e236cde" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MutualFundMember_019e88c3-c07d-7d6a-ab98-ae144b8dcada" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_MutualFundMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InvestmentTypeCategorizationMember_019e88c3-c07d-723e-9974-f3f52e236cde" xlink:to="loc_us-gaap_MutualFundMember_019e88c3-c07d-7d6a-ab98-ae144b8dcada" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockMember_019e88c3-c07d-7b13-a4d2-f8ba900c23ab" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InvestmentTypeCategorizationMember_019e88c3-c07d-723e-9974-f3f52e236cde" xlink:to="loc_us-gaap_CommonStockMember_019e88c3-c07d-7b13-a4d2-f8ba900c23ab" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanCommonCollectiveTrustMember_019e88c3-c07d-7909-a4f1-c1172b5d51a8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DefinedBenefitPlanCommonCollectiveTrustMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InvestmentTypeCategorizationMember_019e88c3-c07d-723e-9974-f3f52e236cde" xlink:to="loc_us-gaap_DefinedBenefitPlanCommonCollectiveTrustMember_019e88c3-c07d-7909-a4f1-c1172b5d51a8" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap-ebp_EmployeeBenefitPlanInvestmentExcludingPlanInterestInMasterTrustFairValue_019e88c3-c07d-719e-bf6c-c86020c3b486" xlink:href="https://xbrl.fasb.org/us-gaap/2026/ebp/elts/us-gaap-ebp-2026.xsd#us-gaap-ebp_EmployeeBenefitPlanInvestmentExcludingPlanInterestInMasterTrustFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap-ebp_EmployeeBenefitPlanInvestmentFairValueAndNavLineItems_019e88c3-c07d-735b-b623-49a37d5e009c" xlink:to="loc_us-gaap-ebp_EmployeeBenefitPlanInvestmentExcludingPlanInterestInMasterTrustFairValue_019e88c3-c07d-719e-bf6c-c86020c3b486" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.mdu.com/role/RelatedPartyandExemptPartyInInterestTransactionsDetails" xlink:type="simple" xlink:href="mdu-20260618.xsd#RelatedPartyandExemptPartyInInterestTransactionsDetails"/>
  <link:definitionLink xlink:role="http://www.mdu.com/role/RelatedPartyandExemptPartyInInterestTransactionsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap-ebp_EmployeeBenefitPlanRelatedPartyAndPartyInInterestTransactionsLineItems_019e88c3-c07d-7e8f-8cc3-a7dd25619c3f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/ebp/elts/us-gaap-ebp-2026.xsd#us-gaap-ebp_EmployeeBenefitPlanRelatedPartyAndPartyInInterestTransactionsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap-ebp_EmployeeBenefitPlanRelatedPartyAndPartyInInterestTransactionsTable_019e88c3-c07d-7103-84b4-9d87a219e500" xlink:href="https://xbrl.fasb.org/us-gaap/2026/ebp/elts/us-gaap-ebp-2026.xsd#us-gaap-ebp_EmployeeBenefitPlanRelatedPartyAndPartyInInterestTransactionsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap-ebp_EmployeeBenefitPlanRelatedPartyAndPartyInInterestTransactionsLineItems_019e88c3-c07d-7e8f-8cc3-a7dd25619c3f" xlink:to="loc_us-gaap-ebp_EmployeeBenefitPlanRelatedPartyAndPartyInInterestTransactionsTable_019e88c3-c07d-7103-84b4-9d87a219e500" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_019e88c3-c07d-7f25-ad90-cf23eca0bf18" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_LegalEntityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap-ebp_EmployeeBenefitPlanRelatedPartyAndPartyInInterestTransactionsTable_019e88c3-c07d-7103-84b4-9d87a219e500" xlink:to="loc_dei_LegalEntityAxis_019e88c3-c07d-7f25-ad90-cf23eca0bf18" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_019e88c3-c07d-7f25-ad90-cf23eca0bf18_default" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_019e88c3-c07d-7f25-ad90-cf23eca0bf18" xlink:to="loc_dei_EntityDomain_019e88c3-c07d-7f25-ad90-cf23eca0bf18_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_019e88c3-c07d-756c-921a-07420dcc29ec" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_019e88c3-c07d-7f25-ad90-cf23eca0bf18" xlink:to="loc_dei_EntityDomain_019e88c3-c07d-756c-921a-07420dcc29ec" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_mdu_EBP004Member_019e88c3-c07d-7d4f-982c-71c8aef16b24" xlink:href="mdu-20260618.xsd#mdu_EBP004Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_019e88c3-c07d-756c-921a-07420dcc29ec" xlink:to="loc_mdu_EBP004Member_019e88c3-c07d-7d4f-982c-71c8aef16b24" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentTypeAxis_019e88c3-c07d-7557-a946-e4bda1ba0055" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InvestmentTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap-ebp_EmployeeBenefitPlanRelatedPartyAndPartyInInterestTransactionsTable_019e88c3-c07d-7103-84b4-9d87a219e500" xlink:to="loc_us-gaap_InvestmentTypeAxis_019e88c3-c07d-7557-a946-e4bda1ba0055" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentTypeCategorizationMember_019e88c3-c07d-7557-a946-e4bda1ba0055_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InvestmentTypeCategorizationMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_InvestmentTypeAxis_019e88c3-c07d-7557-a946-e4bda1ba0055" xlink:to="loc_us-gaap_InvestmentTypeCategorizationMember_019e88c3-c07d-7557-a946-e4bda1ba0055_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentTypeCategorizationMember_019e88c3-c07d-7d81-9740-ccff4eaa345c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InvestmentTypeCategorizationMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_InvestmentTypeAxis_019e88c3-c07d-7557-a946-e4bda1ba0055" xlink:to="loc_us-gaap_InvestmentTypeCategorizationMember_019e88c3-c07d-7d81-9740-ccff4eaa345c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap-ebp_EmployeeBenefitPlanEmployerCommonStockMember_019e88c3-c07d-74f5-8414-f1dd8031f323" xlink:href="https://xbrl.fasb.org/us-gaap/2026/ebp/elts/us-gaap-ebp-2026.xsd#us-gaap-ebp_EmployeeBenefitPlanEmployerCommonStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InvestmentTypeCategorizationMember_019e88c3-c07d-7d81-9740-ccff4eaa345c" xlink:to="loc_us-gaap-ebp_EmployeeBenefitPlanEmployerCommonStockMember_019e88c3-c07d-74f5-8414-f1dd8031f323" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap-ebp_EbpNonemployerCommonStockMember_019eb24f-6f87-7414-8be6-d4b412a614f4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/ebp/elts/us-gaap-ebp-2026.xsd#us-gaap-ebp_EbpNonemployerCommonStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InvestmentTypeCategorizationMember_019e88c3-c07d-7d81-9740-ccff4eaa345c" xlink:to="loc_us-gaap-ebp_EbpNonemployerCommonStockMember_019eb24f-6f87-7414-8be6-d4b412a614f4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap-ebp_EmployeeBenefitPlanInvestmentNumberOfShares_019e88c3-c07d-78e5-8b04-0640b41e6d8f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/ebp/elts/us-gaap-ebp-2026.xsd#us-gaap-ebp_EmployeeBenefitPlanInvestmentNumberOfShares"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap-ebp_EmployeeBenefitPlanRelatedPartyAndPartyInInterestTransactionsLineItems_019e88c3-c07d-7e8f-8cc3-a7dd25619c3f" xlink:to="loc_us-gaap-ebp_EmployeeBenefitPlanInvestmentNumberOfShares_019e88c3-c07d-78e5-8b04-0640b41e6d8f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap-ebp_EmployeeBenefitPlanInvestmentExcludingPlanInterestInMasterTrustFairValue_019e88c3-c07d-7029-99ec-b8d100e005e2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/ebp/elts/us-gaap-ebp-2026.xsd#us-gaap-ebp_EmployeeBenefitPlanInvestmentExcludingPlanInterestInMasterTrustFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap-ebp_EmployeeBenefitPlanRelatedPartyAndPartyInInterestTransactionsLineItems_019e88c3-c07d-7e8f-8cc3-a7dd25619c3f" xlink:to="loc_us-gaap-ebp_EmployeeBenefitPlanInvestmentExcludingPlanInterestInMasterTrustFairValue_019e88c3-c07d-7029-99ec-b8d100e005e2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap-ebp_EmployeeBenefitPlanAssetHeldForInvestmentParticipantLoanAfterDeemedDistribution_019e88c3-c07d-71d8-a55a-8717f6b43bcf" xlink:href="https://xbrl.fasb.org/us-gaap/2026/ebp/elts/us-gaap-ebp-2026.xsd#us-gaap-ebp_EmployeeBenefitPlanAssetHeldForInvestmentParticipantLoanAfterDeemedDistribution"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap-ebp_EmployeeBenefitPlanRelatedPartyAndPartyInInterestTransactionsLineItems_019e88c3-c07d-7e8f-8cc3-a7dd25619c3f" xlink:to="loc_us-gaap-ebp_EmployeeBenefitPlanAssetHeldForInvestmentParticipantLoanAfterDeemedDistribution_019e88c3-c07d-71d8-a55a-8717f6b43bcf" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap-ebp_EmployeeBenefitPlanNoteReceivableFromParticipant_019e88c3-c07d-7c0b-8835-573a32a2d1cf" xlink:href="https://xbrl.fasb.org/us-gaap/2026/ebp/elts/us-gaap-ebp-2026.xsd#us-gaap-ebp_EmployeeBenefitPlanNoteReceivableFromParticipant"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap-ebp_EmployeeBenefitPlanRelatedPartyAndPartyInInterestTransactionsLineItems_019e88c3-c07d-7e8f-8cc3-a7dd25619c3f" xlink:to="loc_us-gaap-ebp_EmployeeBenefitPlanNoteReceivableFromParticipant_019e88c3-c07d-7c0b-8835-573a32a2d1cf" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.mdu.com/role/ReconciliationofFinancialStatementstoForm5500ReconciliationofNetAssetsAvailableforBenefitDetails" xlink:type="simple" xlink:href="mdu-20260618.xsd#ReconciliationofFinancialStatementstoForm5500ReconciliationofNetAssetsAvailableforBenefitDetails"/>
  <link:definitionLink xlink:role="http://www.mdu.com/role/ReconciliationofFinancialStatementstoForm5500ReconciliationofNetAssetsAvailableforBenefitDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap-ebp_EmployeeBenefitPlanReconciliationToForm5500LineItems_019e88c3-c07d-7101-85a3-8219e887ba45" xlink:href="https://xbrl.fasb.org/us-gaap/2026/ebp/elts/us-gaap-ebp-2026.xsd#us-gaap-ebp_EmployeeBenefitPlanReconciliationToForm5500LineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap-ebp_EmployeeBenefitPlanReconciliationToForm5500Table_019e88c3-c07d-7593-8a04-5e471e2c353c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/ebp/elts/us-gaap-ebp-2026.xsd#us-gaap-ebp_EmployeeBenefitPlanReconciliationToForm5500Table"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap-ebp_EmployeeBenefitPlanReconciliationToForm5500LineItems_019e88c3-c07d-7101-85a3-8219e887ba45" xlink:to="loc_us-gaap-ebp_EmployeeBenefitPlanReconciliationToForm5500Table_019e88c3-c07d-7593-8a04-5e471e2c353c" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_019e88c3-c07d-7059-88dc-f145e2cb12e4" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_LegalEntityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap-ebp_EmployeeBenefitPlanReconciliationToForm5500Table_019e88c3-c07d-7593-8a04-5e471e2c353c" xlink:to="loc_dei_LegalEntityAxis_019e88c3-c07d-7059-88dc-f145e2cb12e4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_019e88c3-c07d-7059-88dc-f145e2cb12e4_default" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_019e88c3-c07d-7059-88dc-f145e2cb12e4" xlink:to="loc_dei_EntityDomain_019e88c3-c07d-7059-88dc-f145e2cb12e4_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_019e88c3-c07d-727c-915f-8660504a0685" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_019e88c3-c07d-7059-88dc-f145e2cb12e4" xlink:to="loc_dei_EntityDomain_019e88c3-c07d-727c-915f-8660504a0685" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_mdu_EBP004Member_019e88c3-c07d-708e-925a-4a14251edea2" xlink:href="mdu-20260618.xsd#mdu_EBP004Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_019e88c3-c07d-727c-915f-8660504a0685" xlink:to="loc_mdu_EBP004Member_019e88c3-c07d-708e-925a-4a14251edea2" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap-ebp_EmployeeBenefitPlanNetAssetAvailableForBenefit_019e88c3-c07d-7087-acfa-71b1d024d97c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/ebp/elts/us-gaap-ebp-2026.xsd#us-gaap-ebp_EmployeeBenefitPlanNetAssetAvailableForBenefit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap-ebp_EmployeeBenefitPlanReconciliationToForm5500LineItems_019e88c3-c07d-7101-85a3-8219e887ba45" xlink:to="loc_us-gaap-ebp_EmployeeBenefitPlanNetAssetAvailableForBenefit_019e88c3-c07d-7087-acfa-71b1d024d97c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap-ebp_EmployeeBenefitPlanReconciliationToForm5500NetAssetAvailableForBenefitDeemedDistribution_019e88c3-c07d-75a8-b4b9-8c97cf3822d9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/ebp/elts/us-gaap-ebp-2026.xsd#us-gaap-ebp_EmployeeBenefitPlanReconciliationToForm5500NetAssetAvailableForBenefitDeemedDistribution"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap-ebp_EmployeeBenefitPlanReconciliationToForm5500LineItems_019e88c3-c07d-7101-85a3-8219e887ba45" xlink:to="loc_us-gaap-ebp_EmployeeBenefitPlanReconciliationToForm5500NetAssetAvailableForBenefitDeemedDistribution_019e88c3-c07d-75a8-b4b9-8c97cf3822d9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap-ebp_EmployeeBenefitPlanForm5500CaptionNetAssetAvailableForBenefit_019e88c3-c07d-7a27-a84e-756831c7741b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/ebp/elts/us-gaap-ebp-2026.xsd#us-gaap-ebp_EmployeeBenefitPlanForm5500CaptionNetAssetAvailableForBenefit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap-ebp_EmployeeBenefitPlanReconciliationToForm5500LineItems_019e88c3-c07d-7101-85a3-8219e887ba45" xlink:to="loc_us-gaap-ebp_EmployeeBenefitPlanForm5500CaptionNetAssetAvailableForBenefit_019e88c3-c07d-7a27-a84e-756831c7741b" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.mdu.com/role/ReconciliationofFinancialStatementstoForm5500ReconciliationofNetIncomeDetails" xlink:type="simple" xlink:href="mdu-20260618.xsd#ReconciliationofFinancialStatementstoForm5500ReconciliationofNetIncomeDetails"/>
  <link:definitionLink xlink:role="http://www.mdu.com/role/ReconciliationofFinancialStatementstoForm5500ReconciliationofNetIncomeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap-ebp_EmployeeBenefitPlanReconciliationToForm5500LineItems_019e88c3-c07d-70b5-b712-e501c5ee913a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/ebp/elts/us-gaap-ebp-2026.xsd#us-gaap-ebp_EmployeeBenefitPlanReconciliationToForm5500LineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap-ebp_EmployeeBenefitPlanReconciliationToForm5500Table_019e88c3-c07d-76c2-b4f5-4dd3dfa051de" xlink:href="https://xbrl.fasb.org/us-gaap/2026/ebp/elts/us-gaap-ebp-2026.xsd#us-gaap-ebp_EmployeeBenefitPlanReconciliationToForm5500Table"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap-ebp_EmployeeBenefitPlanReconciliationToForm5500LineItems_019e88c3-c07d-70b5-b712-e501c5ee913a" xlink:to="loc_us-gaap-ebp_EmployeeBenefitPlanReconciliationToForm5500Table_019e88c3-c07d-76c2-b4f5-4dd3dfa051de" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_019e88c3-c07d-7279-8782-0ea34bf97849" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_LegalEntityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap-ebp_EmployeeBenefitPlanReconciliationToForm5500Table_019e88c3-c07d-76c2-b4f5-4dd3dfa051de" xlink:to="loc_dei_LegalEntityAxis_019e88c3-c07d-7279-8782-0ea34bf97849" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_019e88c3-c07d-7279-8782-0ea34bf97849_default" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_019e88c3-c07d-7279-8782-0ea34bf97849" xlink:to="loc_dei_EntityDomain_019e88c3-c07d-7279-8782-0ea34bf97849_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_019e88c3-c07d-78d3-9b16-1c01d9217707" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_019e88c3-c07d-7279-8782-0ea34bf97849" xlink:to="loc_dei_EntityDomain_019e88c3-c07d-78d3-9b16-1c01d9217707" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_mdu_EBP004Member_019e88c3-c07d-7fe0-8943-4abc83fbfb48" xlink:href="mdu-20260618.xsd#mdu_EBP004Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_019e88c3-c07d-78d3-9b16-1c01d9217707" xlink:to="loc_mdu_EBP004Member_019e88c3-c07d-7fe0-8943-4abc83fbfb48" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_mdu_EBPChangeInNetAssetAvailableForBenefitIncludingPlanTransfersIncreaseDecrease_019e88c3-c07d-728a-bcb1-6cb40f8d52f8" xlink:href="mdu-20260618.xsd#mdu_EBPChangeInNetAssetAvailableForBenefitIncludingPlanTransfersIncreaseDecrease"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap-ebp_EmployeeBenefitPlanReconciliationToForm5500LineItems_019e88c3-c07d-70b5-b712-e501c5ee913a" xlink:to="loc_mdu_EBPChangeInNetAssetAvailableForBenefitIncludingPlanTransfersIncreaseDecrease_019e88c3-c07d-728a-bcb1-6cb40f8d52f8" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap-ebp_EmployeeBenefitPlanReconciliationToForm5500ChangeInNetAssetAvailableForBenefitIncreaseDecreaseForDeemedDistribution_019e88c3-c07d-7432-b3df-587025931764" xlink:href="https://xbrl.fasb.org/us-gaap/2026/ebp/elts/us-gaap-ebp-2026.xsd#us-gaap-ebp_EmployeeBenefitPlanReconciliationToForm5500ChangeInNetAssetAvailableForBenefitIncreaseDecreaseForDeemedDistribution"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap-ebp_EmployeeBenefitPlanReconciliationToForm5500LineItems_019e88c3-c07d-70b5-b712-e501c5ee913a" xlink:to="loc_us-gaap-ebp_EmployeeBenefitPlanReconciliationToForm5500ChangeInNetAssetAvailableForBenefitIncreaseDecreaseForDeemedDistribution_019e88c3-c07d-7432-b3df-587025931764" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap-ebp_EmployeeBenefitPlanForm5500CaptionNetIncomeLoss_019e88c3-c07d-7621-9fd2-ca101ecd6307" xlink:href="https://xbrl.fasb.org/us-gaap/2026/ebp/elts/us-gaap-ebp-2026.xsd#us-gaap-ebp_EmployeeBenefitPlanForm5500CaptionNetIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap-ebp_EmployeeBenefitPlanReconciliationToForm5500LineItems_019e88c3-c07d-70b5-b712-e501c5ee913a" xlink:to="loc_us-gaap-ebp_EmployeeBenefitPlanForm5500CaptionNetIncomeLoss_019e88c3-c07d-7621-9fd2-ca101ecd6307" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.mdu.com/role/ScheduleHLine4iScheduleofAssetsHeldAtEndofYearDetails" xlink:type="simple" xlink:href="mdu-20260618.xsd#ScheduleHLine4iScheduleofAssetsHeldAtEndofYearDetails"/>
  <link:definitionLink xlink:role="http://www.mdu.com/role/ScheduleHLine4iScheduleofAssetsHeldAtEndofYearDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap-ebp_EmployeeBenefitPlanScheduleOfAssetHeldForInvestmentLineItems_019e88c3-c07d-71d2-9198-48d17b986e67" xlink:href="https://xbrl.fasb.org/us-gaap/2026/ebp/elts/us-gaap-ebp-2026.xsd#us-gaap-ebp_EmployeeBenefitPlanScheduleOfAssetHeldForInvestmentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap-ebp_EmployeeBenefitPlanScheduleOfAssetHeldForInvestmentTable_019e88c3-c07d-7030-b78e-09e75e381a3f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/ebp/elts/us-gaap-ebp-2026.xsd#us-gaap-ebp_EmployeeBenefitPlanScheduleOfAssetHeldForInvestmentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap-ebp_EmployeeBenefitPlanScheduleOfAssetHeldForInvestmentLineItems_019e88c3-c07d-71d2-9198-48d17b986e67" xlink:to="loc_us-gaap-ebp_EmployeeBenefitPlanScheduleOfAssetHeldForInvestmentTable_019e88c3-c07d-7030-b78e-09e75e381a3f" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_019e88c3-c07d-7fb8-a689-35e4fc708bf3" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_LegalEntityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap-ebp_EmployeeBenefitPlanScheduleOfAssetHeldForInvestmentTable_019e88c3-c07d-7030-b78e-09e75e381a3f" xlink:to="loc_dei_LegalEntityAxis_019e88c3-c07d-7fb8-a689-35e4fc708bf3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_019e88c3-c07d-7fb8-a689-35e4fc708bf3_default" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_019e88c3-c07d-7fb8-a689-35e4fc708bf3" xlink:to="loc_dei_EntityDomain_019e88c3-c07d-7fb8-a689-35e4fc708bf3_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_019e88c3-c07d-7dd9-8991-8f3cd19617ae" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_019e88c3-c07d-7fb8-a689-35e4fc708bf3" xlink:to="loc_dei_EntityDomain_019e88c3-c07d-7dd9-8991-8f3cd19617ae" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_mdu_EBP004Member_019e88c3-c07d-7e43-8538-4d798c9586de" xlink:href="mdu-20260618.xsd#mdu_EBP004Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_019e88c3-c07d-7dd9-8991-8f3cd19617ae" xlink:to="loc_mdu_EBP004Member_019e88c3-c07d-7e43-8538-4d798c9586de" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentIdentifierAxis_019e88c3-c07d-7065-932c-11d3a556dab6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InvestmentIdentifierAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap-ebp_EmployeeBenefitPlanScheduleOfAssetHeldForInvestmentTable_019e88c3-c07d-7030-b78e-09e75e381a3f" xlink:to="loc_us-gaap_InvestmentIdentifierAxis_019e88c3-c07d-7065-932c-11d3a556dab6" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentTypeAxis_019e88c3-c07d-7c92-8932-d8ed08811a75" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InvestmentTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap-ebp_EmployeeBenefitPlanScheduleOfAssetHeldForInvestmentTable_019e88c3-c07d-7030-b78e-09e75e381a3f" xlink:to="loc_us-gaap_InvestmentTypeAxis_019e88c3-c07d-7c92-8932-d8ed08811a75" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentTypeCategorizationMember_019e88c3-c07d-7c92-8932-d8ed08811a75_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InvestmentTypeCategorizationMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_InvestmentTypeAxis_019e88c3-c07d-7c92-8932-d8ed08811a75" xlink:to="loc_us-gaap_InvestmentTypeCategorizationMember_019e88c3-c07d-7c92-8932-d8ed08811a75_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentTypeCategorizationMember_019e88c3-c07d-724c-aeb4-0a5386929bf6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InvestmentTypeCategorizationMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_InvestmentTypeAxis_019e88c3-c07d-7c92-8932-d8ed08811a75" xlink:to="loc_us-gaap_InvestmentTypeCategorizationMember_019e88c3-c07d-724c-aeb4-0a5386929bf6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap-ebp_EmployeeBenefitPlanEmployerCommonStockMember_019e88c3-c07d-75dc-8fc1-4049886a3f9f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/ebp/elts/us-gaap-ebp-2026.xsd#us-gaap-ebp_EmployeeBenefitPlanEmployerCommonStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InvestmentTypeCategorizationMember_019e88c3-c07d-724c-aeb4-0a5386929bf6" xlink:to="loc_us-gaap-ebp_EmployeeBenefitPlanEmployerCommonStockMember_019e88c3-c07d-75dc-8fc1-4049886a3f9f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_019eadf0-cde6-7b2c-8d11-9532cacdb55e" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap-ebp_EmployeeBenefitPlanScheduleOfAssetHeldForInvestmentTable_019e88c3-c07d-7030-b78e-09e75e381a3f" xlink:to="loc_srt_RangeAxis_019eadf0-cde6-7b2c-8d11-9532cacdb55e" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_019eadf0-cde6-7b2c-8d11-9532cacdb55e_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_019eadf0-cde6-7b2c-8d11-9532cacdb55e" xlink:to="loc_srt_RangeMember_019eadf0-cde6-7b2c-8d11-9532cacdb55e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_019eadf0-cde6-7ba0-a630-3ea043296e65" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_019eadf0-cde6-7b2c-8d11-9532cacdb55e" xlink:to="loc_srt_RangeMember_019eadf0-cde6-7ba0-a630-3ea043296e65" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_019eadf0-cde6-7e35-b9bd-8665a35bcf75" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_019eadf0-cde6-7ba0-a630-3ea043296e65" xlink:to="loc_srt_MaximumMember_019eadf0-cde6-7e35-b9bd-8665a35bcf75" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_019eadf0-ebe9-78f9-bb12-00fd00888c7f" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_019eadf0-cde6-7ba0-a630-3ea043296e65" xlink:to="loc_srt_MinimumMember_019eadf0-ebe9-78f9-bb12-00fd00888c7f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityTaxIdentificationNumber_019e88c3-c07d-7400-9dc0-b0dbe1d67844" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityTaxIdentificationNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap-ebp_EmployeeBenefitPlanScheduleOfAssetHeldForInvestmentLineItems_019e88c3-c07d-71d2-9198-48d17b986e67" xlink:to="loc_dei_EntityTaxIdentificationNumber_019e88c3-c07d-7400-9dc0-b0dbe1d67844" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap-ebp_EmployeeBenefitPlanPlanNumber_019e88c3-c07d-74e4-8144-5595789a4e5d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/ebp/elts/us-gaap-ebp-2026.xsd#us-gaap-ebp_EmployeeBenefitPlanPlanNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap-ebp_EmployeeBenefitPlanScheduleOfAssetHeldForInvestmentLineItems_019e88c3-c07d-71d2-9198-48d17b986e67" xlink:to="loc_us-gaap-ebp_EmployeeBenefitPlanPlanNumber_019e88c3-c07d-74e4-8144-5595789a4e5d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap-ebp_EmployeeBenefitPlanAssetHeldForInvestmentInvestmentExcludingPlanInterestInMasterTrustCurrentValue_019e88c3-c07d-7a27-97ec-2c59509dc166" xlink:href="https://xbrl.fasb.org/us-gaap/2026/ebp/elts/us-gaap-ebp-2026.xsd#us-gaap-ebp_EmployeeBenefitPlanAssetHeldForInvestmentInvestmentExcludingPlanInterestInMasterTrustCurrentValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap-ebp_EmployeeBenefitPlanScheduleOfAssetHeldForInvestmentLineItems_019e88c3-c07d-71d2-9198-48d17b986e67" xlink:to="loc_us-gaap-ebp_EmployeeBenefitPlanAssetHeldForInvestmentInvestmentExcludingPlanInterestInMasterTrustCurrentValue_019e88c3-c07d-7a27-97ec-2c59509dc166" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap-ebp_EmployeeBenefitPlanAssetHeldForInvestmentParticipantLoanAfterDeemedDistribution_019e88c3-c07d-7857-adc9-c24b5c64c363" xlink:href="https://xbrl.fasb.org/us-gaap/2026/ebp/elts/us-gaap-ebp-2026.xsd#us-gaap-ebp_EmployeeBenefitPlanAssetHeldForInvestmentParticipantLoanAfterDeemedDistribution"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap-ebp_EmployeeBenefitPlanScheduleOfAssetHeldForInvestmentLineItems_019e88c3-c07d-71d2-9198-48d17b986e67" xlink:to="loc_us-gaap-ebp_EmployeeBenefitPlanAssetHeldForInvestmentParticipantLoanAfterDeemedDistribution_019e88c3-c07d-7857-adc9-c24b5c64c363" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap-ebp_EmployeeBenefitPlanAssetHeldForInvestment_019eb250-7118-7375-8154-d986bc648724" xlink:href="https://xbrl.fasb.org/us-gaap/2026/ebp/elts/us-gaap-ebp-2026.xsd#us-gaap-ebp_EmployeeBenefitPlanAssetHeldForInvestment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap-ebp_EmployeeBenefitPlanScheduleOfAssetHeldForInvestmentLineItems_019e88c3-c07d-71d2-9198-48d17b986e67" xlink:to="loc_us-gaap-ebp_EmployeeBenefitPlanAssetHeldForInvestment_019eb250-7118-7375-8154-d986bc648724" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap-ebp_EmployeeBenefitPlanReconciliationToForm5500NetAssetAvailableForBenefitDeemedDistribution_019eadf2-2c43-7ab6-b42d-ab4487c30022" xlink:href="https://xbrl.fasb.org/us-gaap/2026/ebp/elts/us-gaap-ebp-2026.xsd#us-gaap-ebp_EmployeeBenefitPlanReconciliationToForm5500NetAssetAvailableForBenefitDeemedDistribution"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap-ebp_EmployeeBenefitPlanScheduleOfAssetHeldForInvestmentLineItems_019e88c3-c07d-71d2-9198-48d17b986e67" xlink:to="loc_us-gaap-ebp_EmployeeBenefitPlanReconciliationToForm5500NetAssetAvailableForBenefitDeemedDistribution_019eadf2-2c43-7ab6-b42d-ab4487c30022" xlink:type="arc" order="5"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.mdu.com/role/ScheduleHLine4iScheduleofAssetsHeldAtEndofYearDetails_1" xlink:type="simple" xlink:href="mdu-20260618.xsd#ScheduleHLine4iScheduleofAssetsHeldAtEndofYearDetails_1"/>
  <link:definitionLink xlink:role="http://www.mdu.com/role/ScheduleHLine4iScheduleofAssetsHeldAtEndofYearDetails_1" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap-ebp_EmployeeBenefitPlanScheduleOfAssetHeldForInvestmentLineItems_019e88c3-c07d-71d2-9198-48d17b986e67" xlink:href="https://xbrl.fasb.org/us-gaap/2026/ebp/elts/us-gaap-ebp-2026.xsd#us-gaap-ebp_EmployeeBenefitPlanScheduleOfAssetHeldForInvestmentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap-ebp_EmployeeBenefitPlanScheduleOfAssetHeldForInvestmentTable_019e88c3-c07d-7030-b78e-09e75e381a3f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/ebp/elts/us-gaap-ebp-2026.xsd#us-gaap-ebp_EmployeeBenefitPlanScheduleOfAssetHeldForInvestmentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap-ebp_EmployeeBenefitPlanScheduleOfAssetHeldForInvestmentLineItems_019e88c3-c07d-71d2-9198-48d17b986e67" xlink:to="loc_us-gaap-ebp_EmployeeBenefitPlanScheduleOfAssetHeldForInvestmentTable_019e88c3-c07d-7030-b78e-09e75e381a3f" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_019e88c3-c07d-7fb8-a689-35e4fc708bf3" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_LegalEntityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap-ebp_EmployeeBenefitPlanScheduleOfAssetHeldForInvestmentTable_019e88c3-c07d-7030-b78e-09e75e381a3f" xlink:to="loc_dei_LegalEntityAxis_019e88c3-c07d-7fb8-a689-35e4fc708bf3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_019e88c3-c07d-7fb8-a689-35e4fc708bf3_default" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_019e88c3-c07d-7fb8-a689-35e4fc708bf3" xlink:to="loc_dei_EntityDomain_019e88c3-c07d-7fb8-a689-35e4fc708bf3_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_019e88c3-c07d-7dd9-8991-8f3cd19617ae" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_019e88c3-c07d-7fb8-a689-35e4fc708bf3" xlink:to="loc_dei_EntityDomain_019e88c3-c07d-7dd9-8991-8f3cd19617ae" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_mdu_EBP004Member_019e88c3-c07d-7e43-8538-4d798c9586de" xlink:href="mdu-20260618.xsd#mdu_EBP004Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_019e88c3-c07d-7dd9-8991-8f3cd19617ae" xlink:to="loc_mdu_EBP004Member_019e88c3-c07d-7e43-8538-4d798c9586de" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentTypeAxis_019e88c3-c07d-7c92-8932-d8ed08811a75" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InvestmentTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap-ebp_EmployeeBenefitPlanScheduleOfAssetHeldForInvestmentTable_019e88c3-c07d-7030-b78e-09e75e381a3f" xlink:to="loc_us-gaap_InvestmentTypeAxis_019e88c3-c07d-7c92-8932-d8ed08811a75" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentTypeCategorizationMember_019e88c3-c07d-7c92-8932-d8ed08811a75_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InvestmentTypeCategorizationMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_InvestmentTypeAxis_019e88c3-c07d-7c92-8932-d8ed08811a75" xlink:to="loc_us-gaap_InvestmentTypeCategorizationMember_019e88c3-c07d-7c92-8932-d8ed08811a75_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentTypeCategorizationMember_019e88c3-c07d-724c-aeb4-0a5386929bf6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InvestmentTypeCategorizationMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_InvestmentTypeAxis_019e88c3-c07d-7c92-8932-d8ed08811a75" xlink:to="loc_us-gaap_InvestmentTypeCategorizationMember_019e88c3-c07d-724c-aeb4-0a5386929bf6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap-ebp_EmployeeBenefitPlanEmployerCommonStockMember_019e88c3-c07d-75dc-8fc1-4049886a3f9f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/ebp/elts/us-gaap-ebp-2026.xsd#us-gaap-ebp_EmployeeBenefitPlanEmployerCommonStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InvestmentTypeCategorizationMember_019e88c3-c07d-724c-aeb4-0a5386929bf6" xlink:to="loc_us-gaap-ebp_EmployeeBenefitPlanEmployerCommonStockMember_019e88c3-c07d-75dc-8fc1-4049886a3f9f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_019eadf0-cde6-7b2c-8d11-9532cacdb55e" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap-ebp_EmployeeBenefitPlanScheduleOfAssetHeldForInvestmentTable_019e88c3-c07d-7030-b78e-09e75e381a3f" xlink:to="loc_srt_RangeAxis_019eadf0-cde6-7b2c-8d11-9532cacdb55e" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_019eadf0-cde6-7b2c-8d11-9532cacdb55e_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_019eadf0-cde6-7b2c-8d11-9532cacdb55e" xlink:to="loc_srt_RangeMember_019eadf0-cde6-7b2c-8d11-9532cacdb55e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_019eadf0-cde6-7ba0-a630-3ea043296e65" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_019eadf0-cde6-7b2c-8d11-9532cacdb55e" xlink:to="loc_srt_RangeMember_019eadf0-cde6-7ba0-a630-3ea043296e65" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_019eadf0-cde6-7e35-b9bd-8665a35bcf75" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_019eadf0-cde6-7ba0-a630-3ea043296e65" xlink:to="loc_srt_MaximumMember_019eadf0-cde6-7e35-b9bd-8665a35bcf75" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_019eadf0-ebe9-78f9-bb12-00fd00888c7f" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_019eadf0-cde6-7ba0-a630-3ea043296e65" xlink:to="loc_srt_MinimumMember_019eadf0-ebe9-78f9-bb12-00fd00888c7f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityTaxIdentificationNumber_019e88c3-c07d-7400-9dc0-b0dbe1d67844" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityTaxIdentificationNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap-ebp_EmployeeBenefitPlanScheduleOfAssetHeldForInvestmentLineItems_019e88c3-c07d-71d2-9198-48d17b986e67" xlink:to="loc_dei_EntityTaxIdentificationNumber_019e88c3-c07d-7400-9dc0-b0dbe1d67844" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap-ebp_EmployeeBenefitPlanPlanNumber_019e88c3-c07d-74e4-8144-5595789a4e5d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/ebp/elts/us-gaap-ebp-2026.xsd#us-gaap-ebp_EmployeeBenefitPlanPlanNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap-ebp_EmployeeBenefitPlanScheduleOfAssetHeldForInvestmentLineItems_019e88c3-c07d-71d2-9198-48d17b986e67" xlink:to="loc_us-gaap-ebp_EmployeeBenefitPlanPlanNumber_019e88c3-c07d-74e4-8144-5595789a4e5d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap-ebp_EmployeeBenefitPlanAssetHeldForInvestmentInvestmentExcludingPlanInterestInMasterTrustCurrentValue_019e88c3-c07d-7a27-97ec-2c59509dc166" xlink:href="https://xbrl.fasb.org/us-gaap/2026/ebp/elts/us-gaap-ebp-2026.xsd#us-gaap-ebp_EmployeeBenefitPlanAssetHeldForInvestmentInvestmentExcludingPlanInterestInMasterTrustCurrentValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap-ebp_EmployeeBenefitPlanScheduleOfAssetHeldForInvestmentLineItems_019e88c3-c07d-71d2-9198-48d17b986e67" xlink:to="loc_us-gaap-ebp_EmployeeBenefitPlanAssetHeldForInvestmentInvestmentExcludingPlanInterestInMasterTrustCurrentValue_019e88c3-c07d-7a27-97ec-2c59509dc166" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap-ebp_EmployeeBenefitPlanAssetHeldForInvestmentParticipantLoanAfterDeemedDistribution_019e88c3-c07d-7857-adc9-c24b5c64c363" xlink:href="https://xbrl.fasb.org/us-gaap/2026/ebp/elts/us-gaap-ebp-2026.xsd#us-gaap-ebp_EmployeeBenefitPlanAssetHeldForInvestmentParticipantLoanAfterDeemedDistribution"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap-ebp_EmployeeBenefitPlanScheduleOfAssetHeldForInvestmentLineItems_019e88c3-c07d-71d2-9198-48d17b986e67" xlink:to="loc_us-gaap-ebp_EmployeeBenefitPlanAssetHeldForInvestmentParticipantLoanAfterDeemedDistribution_019e88c3-c07d-7857-adc9-c24b5c64c363" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap-ebp_EmployeeBenefitPlanAssetHeldForInvestment_019eb250-7118-7375-8154-d986bc648724" xlink:href="https://xbrl.fasb.org/us-gaap/2026/ebp/elts/us-gaap-ebp-2026.xsd#us-gaap-ebp_EmployeeBenefitPlanAssetHeldForInvestment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap-ebp_EmployeeBenefitPlanScheduleOfAssetHeldForInvestmentLineItems_019e88c3-c07d-71d2-9198-48d17b986e67" xlink:to="loc_us-gaap-ebp_EmployeeBenefitPlanAssetHeldForInvestment_019eb250-7118-7375-8154-d986bc648724" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap-ebp_EmployeeBenefitPlanReconciliationToForm5500NetAssetAvailableForBenefitDeemedDistribution_019eadf2-2c43-7ab6-b42d-ab4487c30022" xlink:href="https://xbrl.fasb.org/us-gaap/2026/ebp/elts/us-gaap-ebp-2026.xsd#us-gaap-ebp_EmployeeBenefitPlanReconciliationToForm5500NetAssetAvailableForBenefitDeemedDistribution"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap-ebp_EmployeeBenefitPlanScheduleOfAssetHeldForInvestmentLineItems_019e88c3-c07d-71d2-9198-48d17b986e67" xlink:to="loc_us-gaap-ebp_EmployeeBenefitPlanReconciliationToForm5500NetAssetAvailableForBenefitDeemedDistribution_019eadf2-2c43-7ab6-b42d-ab4487c30022" xlink:type="arc" order="5"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.mdu.com/role/ScheduleHLine4iScheduleofAssetsAcquiredandDisposedofWithinYearDetails" xlink:type="simple" xlink:href="mdu-20260618.xsd#ScheduleHLine4iScheduleofAssetsAcquiredandDisposedofWithinYearDetails"/>
  <link:definitionLink xlink:role="http://www.mdu.com/role/ScheduleHLine4iScheduleofAssetsAcquiredandDisposedofWithinYearDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap-ebp_EmployeeBenefitPlanScheduleOfAssetAcquiredAndDisposedLineItems_019e88c3-c07d-7c3a-a692-23c5c78fb5a0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/ebp/elts/us-gaap-ebp-2026.xsd#us-gaap-ebp_EmployeeBenefitPlanScheduleOfAssetAcquiredAndDisposedLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap-ebp_EmployeeBenefitPlanScheduleOfAssetAcquiredAndDisposedTable_019e88c3-c07d-783c-88a7-346dc21a83e0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/ebp/elts/us-gaap-ebp-2026.xsd#us-gaap-ebp_EmployeeBenefitPlanScheduleOfAssetAcquiredAndDisposedTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap-ebp_EmployeeBenefitPlanScheduleOfAssetAcquiredAndDisposedLineItems_019e88c3-c07d-7c3a-a692-23c5c78fb5a0" xlink:to="loc_us-gaap-ebp_EmployeeBenefitPlanScheduleOfAssetAcquiredAndDisposedTable_019e88c3-c07d-783c-88a7-346dc21a83e0" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentIdentifierAxis_019e88c3-c07d-7dcd-b241-3bd5b929e3c9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InvestmentIdentifierAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap-ebp_EmployeeBenefitPlanScheduleOfAssetAcquiredAndDisposedTable_019e88c3-c07d-783c-88a7-346dc21a83e0" xlink:to="loc_us-gaap_InvestmentIdentifierAxis_019e88c3-c07d-7dcd-b241-3bd5b929e3c9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_019e88c3-c07d-7db4-9ff2-3e8561abfdd6" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_LegalEntityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap-ebp_EmployeeBenefitPlanScheduleOfAssetAcquiredAndDisposedTable_019e88c3-c07d-783c-88a7-346dc21a83e0" xlink:to="loc_dei_LegalEntityAxis_019e88c3-c07d-7db4-9ff2-3e8561abfdd6" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_019e88c3-c07d-7db4-9ff2-3e8561abfdd6_default" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_019e88c3-c07d-7db4-9ff2-3e8561abfdd6" xlink:to="loc_dei_EntityDomain_019e88c3-c07d-7db4-9ff2-3e8561abfdd6_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_019e88c3-c07d-7a64-a89b-654773f3291a" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_019e88c3-c07d-7db4-9ff2-3e8561abfdd6" xlink:to="loc_dei_EntityDomain_019e88c3-c07d-7a64-a89b-654773f3291a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_mdu_EBP004Member_019e88c3-c07d-7b16-bcce-f4400db0ff8c" xlink:href="mdu-20260618.xsd#mdu_EBP004Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_019e88c3-c07d-7a64-a89b-654773f3291a" xlink:to="loc_mdu_EBP004Member_019e88c3-c07d-7b16-bcce-f4400db0ff8c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019ea84e-fe31-770f-9bd1-f1a31f4606a6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap-ebp_EmployeeBenefitPlanScheduleOfAssetAcquiredAndDisposedTable_019e88c3-c07d-783c-88a7-346dc21a83e0" xlink:to="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019ea84e-fe31-770f-9bd1-f1a31f4606a6" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019ea84e-fe31-770f-9bd1-f1a31f4606a6_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019ea84e-fe31-770f-9bd1-f1a31f4606a6" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019ea84e-fe31-770f-9bd1-f1a31f4606a6_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019ea84e-fe31-7f59-b0e2-7876e91ec892" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019ea84e-fe31-770f-9bd1-f1a31f4606a6" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019ea84e-fe31-7f59-b0e2-7876e91ec892" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasuredAtNetAssetValuePerShareMember_019ea84e-fe31-79de-bd85-37612a446cb8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueMeasuredAtNetAssetValuePerShareMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019ea84e-fe31-7f59-b0e2-7876e91ec892" xlink:to="loc_us-gaap_FairValueMeasuredAtNetAssetValuePerShareMember_019ea84e-fe31-79de-bd85-37612a446cb8" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentTypeAxis_019ea84e-fe31-733d-ac8a-94211b9f8755" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InvestmentTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap-ebp_EmployeeBenefitPlanScheduleOfAssetAcquiredAndDisposedTable_019e88c3-c07d-783c-88a7-346dc21a83e0" xlink:to="loc_us-gaap_InvestmentTypeAxis_019ea84e-fe31-733d-ac8a-94211b9f8755" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentTypeCategorizationMember_019ea84e-fe31-733d-ac8a-94211b9f8755_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InvestmentTypeCategorizationMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_InvestmentTypeAxis_019ea84e-fe31-733d-ac8a-94211b9f8755" xlink:to="loc_us-gaap_InvestmentTypeCategorizationMember_019ea84e-fe31-733d-ac8a-94211b9f8755_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentTypeCategorizationMember_019ea84e-fe31-774f-a86b-c07fd27b3f6f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InvestmentTypeCategorizationMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_InvestmentTypeAxis_019ea84e-fe31-733d-ac8a-94211b9f8755" xlink:to="loc_us-gaap_InvestmentTypeCategorizationMember_019ea84e-fe31-774f-a86b-c07fd27b3f6f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanCommonCollectiveTrustMember_019ea84e-fe31-7971-a81c-caa691f8abb3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DefinedBenefitPlanCommonCollectiveTrustMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InvestmentTypeCategorizationMember_019ea84e-fe31-774f-a86b-c07fd27b3f6f" xlink:to="loc_us-gaap_DefinedBenefitPlanCommonCollectiveTrustMember_019ea84e-fe31-7971-a81c-caa691f8abb3" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityTaxIdentificationNumber_019e88c3-c07d-731f-8732-3b94eb9c114e" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityTaxIdentificationNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap-ebp_EmployeeBenefitPlanScheduleOfAssetAcquiredAndDisposedLineItems_019e88c3-c07d-7c3a-a692-23c5c78fb5a0" xlink:to="loc_dei_EntityTaxIdentificationNumber_019e88c3-c07d-731f-8732-3b94eb9c114e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap-ebp_EmployeeBenefitPlanPlanNumber_019e88c3-c07d-7e5b-b9f4-e12d671f39b4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/ebp/elts/us-gaap-ebp-2026.xsd#us-gaap-ebp_EmployeeBenefitPlanPlanNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap-ebp_EmployeeBenefitPlanScheduleOfAssetAcquiredAndDisposedLineItems_019e88c3-c07d-7c3a-a692-23c5c78fb5a0" xlink:to="loc_us-gaap-ebp_EmployeeBenefitPlanPlanNumber_019e88c3-c07d-7e5b-b9f4-e12d671f39b4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap-ebp_EmployeeBenefitPlanInvestmentExcludingPlanInterestInMasterTrustFairValue_019ea84e-fe31-75d2-9cc7-f75e9df059a1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/ebp/elts/us-gaap-ebp-2026.xsd#us-gaap-ebp_EmployeeBenefitPlanInvestmentExcludingPlanInterestInMasterTrustFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap-ebp_EmployeeBenefitPlanScheduleOfAssetAcquiredAndDisposedLineItems_019e88c3-c07d-7c3a-a692-23c5c78fb5a0" xlink:to="loc_us-gaap-ebp_EmployeeBenefitPlanInvestmentExcludingPlanInterestInMasterTrustFairValue_019ea84e-fe31-75d2-9cc7-f75e9df059a1" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.mdu.com/role/ScheduleHLine4iScheduleofAssetsAcquiredandDisposedofWithinYearDetails_1" xlink:type="simple" xlink:href="mdu-20260618.xsd#ScheduleHLine4iScheduleofAssetsAcquiredandDisposedofWithinYearDetails_1"/>
  <link:definitionLink xlink:role="http://www.mdu.com/role/ScheduleHLine4iScheduleofAssetsAcquiredandDisposedofWithinYearDetails_1" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap-ebp_EmployeeBenefitPlanScheduleOfAssetAcquiredAndDisposedLineItems_019e88c3-c07d-7c3a-a692-23c5c78fb5a0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/ebp/elts/us-gaap-ebp-2026.xsd#us-gaap-ebp_EmployeeBenefitPlanScheduleOfAssetAcquiredAndDisposedLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap-ebp_EmployeeBenefitPlanScheduleOfAssetAcquiredAndDisposedTable_019e88c3-c07d-783c-88a7-346dc21a83e0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/ebp/elts/us-gaap-ebp-2026.xsd#us-gaap-ebp_EmployeeBenefitPlanScheduleOfAssetAcquiredAndDisposedTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap-ebp_EmployeeBenefitPlanScheduleOfAssetAcquiredAndDisposedLineItems_019e88c3-c07d-7c3a-a692-23c5c78fb5a0" xlink:to="loc_us-gaap-ebp_EmployeeBenefitPlanScheduleOfAssetAcquiredAndDisposedTable_019e88c3-c07d-783c-88a7-346dc21a83e0" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_019e88c3-c07d-7db4-9ff2-3e8561abfdd6" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_LegalEntityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap-ebp_EmployeeBenefitPlanScheduleOfAssetAcquiredAndDisposedTable_019e88c3-c07d-783c-88a7-346dc21a83e0" xlink:to="loc_dei_LegalEntityAxis_019e88c3-c07d-7db4-9ff2-3e8561abfdd6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_019e88c3-c07d-7db4-9ff2-3e8561abfdd6_default" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_019e88c3-c07d-7db4-9ff2-3e8561abfdd6" xlink:to="loc_dei_EntityDomain_019e88c3-c07d-7db4-9ff2-3e8561abfdd6_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_019e88c3-c07d-7a64-a89b-654773f3291a" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_019e88c3-c07d-7db4-9ff2-3e8561abfdd6" xlink:to="loc_dei_EntityDomain_019e88c3-c07d-7a64-a89b-654773f3291a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_mdu_EBP004Member_019e88c3-c07d-7b16-bcce-f4400db0ff8c" xlink:href="mdu-20260618.xsd#mdu_EBP004Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_019e88c3-c07d-7a64-a89b-654773f3291a" xlink:to="loc_mdu_EBP004Member_019e88c3-c07d-7b16-bcce-f4400db0ff8c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019ea84e-fe31-770f-9bd1-f1a31f4606a6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap-ebp_EmployeeBenefitPlanScheduleOfAssetAcquiredAndDisposedTable_019e88c3-c07d-783c-88a7-346dc21a83e0" xlink:to="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019ea84e-fe31-770f-9bd1-f1a31f4606a6" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019ea84e-fe31-770f-9bd1-f1a31f4606a6_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019ea84e-fe31-770f-9bd1-f1a31f4606a6" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019ea84e-fe31-770f-9bd1-f1a31f4606a6_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019ea84e-fe31-7f59-b0e2-7876e91ec892" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019ea84e-fe31-770f-9bd1-f1a31f4606a6" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019ea84e-fe31-7f59-b0e2-7876e91ec892" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasuredAtNetAssetValuePerShareMember_019ea84e-fe31-79de-bd85-37612a446cb8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueMeasuredAtNetAssetValuePerShareMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019ea84e-fe31-7f59-b0e2-7876e91ec892" xlink:to="loc_us-gaap_FairValueMeasuredAtNetAssetValuePerShareMember_019ea84e-fe31-79de-bd85-37612a446cb8" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentTypeAxis_019ea84e-fe31-733d-ac8a-94211b9f8755" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InvestmentTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap-ebp_EmployeeBenefitPlanScheduleOfAssetAcquiredAndDisposedTable_019e88c3-c07d-783c-88a7-346dc21a83e0" xlink:to="loc_us-gaap_InvestmentTypeAxis_019ea84e-fe31-733d-ac8a-94211b9f8755" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentTypeCategorizationMember_019ea84e-fe31-733d-ac8a-94211b9f8755_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InvestmentTypeCategorizationMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_InvestmentTypeAxis_019ea84e-fe31-733d-ac8a-94211b9f8755" xlink:to="loc_us-gaap_InvestmentTypeCategorizationMember_019ea84e-fe31-733d-ac8a-94211b9f8755_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentTypeCategorizationMember_019ea84e-fe31-774f-a86b-c07fd27b3f6f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InvestmentTypeCategorizationMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_InvestmentTypeAxis_019ea84e-fe31-733d-ac8a-94211b9f8755" xlink:to="loc_us-gaap_InvestmentTypeCategorizationMember_019ea84e-fe31-774f-a86b-c07fd27b3f6f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanCommonCollectiveTrustMember_019ea84e-fe31-7971-a81c-caa691f8abb3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DefinedBenefitPlanCommonCollectiveTrustMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InvestmentTypeCategorizationMember_019ea84e-fe31-774f-a86b-c07fd27b3f6f" xlink:to="loc_us-gaap_DefinedBenefitPlanCommonCollectiveTrustMember_019ea84e-fe31-7971-a81c-caa691f8abb3" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityTaxIdentificationNumber_019e88c3-c07d-731f-8732-3b94eb9c114e" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityTaxIdentificationNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap-ebp_EmployeeBenefitPlanScheduleOfAssetAcquiredAndDisposedLineItems_019e88c3-c07d-7c3a-a692-23c5c78fb5a0" xlink:to="loc_dei_EntityTaxIdentificationNumber_019e88c3-c07d-731f-8732-3b94eb9c114e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap-ebp_EmployeeBenefitPlanPlanNumber_019e88c3-c07d-7e5b-b9f4-e12d671f39b4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/ebp/elts/us-gaap-ebp-2026.xsd#us-gaap-ebp_EmployeeBenefitPlanPlanNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap-ebp_EmployeeBenefitPlanScheduleOfAssetAcquiredAndDisposedLineItems_019e88c3-c07d-7c3a-a692-23c5c78fb5a0" xlink:to="loc_us-gaap-ebp_EmployeeBenefitPlanPlanNumber_019e88c3-c07d-7e5b-b9f4-e12d671f39b4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap-ebp_EmployeeBenefitPlanInvestmentExcludingPlanInterestInMasterTrustFairValue_019ea84e-fe31-75d2-9cc7-f75e9df059a1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/ebp/elts/us-gaap-ebp-2026.xsd#us-gaap-ebp_EmployeeBenefitPlanInvestmentExcludingPlanInterestInMasterTrustFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap-ebp_EmployeeBenefitPlanScheduleOfAssetAcquiredAndDisposedLineItems_019e88c3-c07d-7c3a-a692-23c5c78fb5a0" xlink:to="loc_us-gaap-ebp_EmployeeBenefitPlanInvestmentExcludingPlanInterestInMasterTrustFairValue_019ea84e-fe31-75d2-9cc7-f75e9df059a1" xlink:type="arc" order="2"/>
  </link:definitionLink>
</link:linkbase>
