content: <?xml version="1.0" encoding="UTF-8"?><edgarSubmission xmlns="http://www.sec.gov/edgar/ownership" xmlns:com="http://www.sec.gov/edgar/common">
    <headerData>
      <submissionType>144</submissionType>
      <filerInfo>
        <filer>
          <filerCredentials>
            <cik>0001408733</cik>
            <ccc>XXXXXXXX</ccc>
          </filerCredentials>
        </filer>
        <liveTestFlag>LIVE</liveTestFlag>
  
  
  
      </filerInfo>
    </headerData>
    <formData>
      <issuerInfo>
        <issuerCik>0000860413</issuerCik>
        <issuerName>FIRST INTERSTATE BANCSYSTEM INC</issuerName>
        <secFileNumber>001-34653</secFileNumber>
        <issuerAddress>
          <com:street1>401 NO 31ST STREET</com:street1>
          <com:city>BILLINGS</com:city>
          <com:stateOrCountry>MT</com:stateOrCountry>
          <com:zipCode>59101</com:zipCode>
        </issuerAddress>
        <issuerContactPhone>4062555311</issuerContactPhone>
        <nameOfPersonForWhoseAccountTheSecuritiesAreToBeSold>RILEY KEVIN P</nameOfPersonForWhoseAccountTheSecuritiesAreToBeSold>
        <relationshipsToIssuer>
          <relationshipToIssuer>Officer</relationshipToIssuer>
          <relationshipToIssuer>Director</relationshipToIssuer>
        </relationshipsToIssuer>
      </issuerInfo>
      <securitiesInformation>
        <securitiesClassTitle>Common</securitiesClassTitle>
        <brokerOrMarketmakerDetails>
          <name>Fidelity Brokerage Services LLC</name>
          <address>
            <com:street1>900 Salem Street</com:street1>
            <com:city>Smithfield</com:city>
            <com:stateOrCountry>RI</com:stateOrCountry>
            <com:zipCode>02917</com:zipCode>
          </address>
        </brokerOrMarketmakerDetails>
        <noOfUnitsSold>7300</noOfUnitsSold>
        <aggregateMarketValue>217613.73</aggregateMarketValue>
        <noOfUnitsOutstanding>104568019</noOfUnitsOutstanding>
        <approxSaleDate>08/01/2024</approxSaleDate>
        <securitiesExchangeName>NASDAQ</securitiesExchangeName>
      </securitiesInformation>
      <securitiesToBeSold>
        <securitiesClassTitle>Common</securitiesClassTitle>
        <acquiredDate>03/15/2024</acquiredDate>
        <natureOfAcquisitionTransaction>Restricted Stock Vesting</natureOfAcquisitionTransaction>
        <nameOfPersonfromWhomAcquired>Issuer</nameOfPersonfromWhomAcquired>
        <isGiftTransaction>N</isGiftTransaction>
        <amountOfSecuritiesAcquired>7300</amountOfSecuritiesAcquired>
        <paymentDate>03/15/2024</paymentDate>
        <natureOfPayment>Compensation</natureOfPayment>
      </securitiesToBeSold>
      <nothingToReportFlagOnSecuritiesSoldInPast3Months>Y</nothingToReportFlagOnSecuritiesSoldInPast3Months>
      <noticeSignature>
        <noticeDate>08/01/2024</noticeDate>
        <signature>/s/ Daniel Tucci, as a duly authorized representative of Fidelity Brokerage Services LLC, as attorney-in-fact for Kevin Riley</signature>
      </noticeSignature>
    </formData>
  </edgarSubmission>
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text: 144
  0001408733
  XXXXXXXX
  LIVE
  0000860413
  FIRST INTERSTATE BANCSYSTEM INC
  001-34653
  401 NO 31ST STREET
  BILLINGS
  MT
  59101
  4062555311
  RILEY KEVIN P
  Officer
  Director
  Common
  Fidelity Brokerage Services LLC
  900 Salem Street
  Smithfield
  RI
  02917
  7300
  217613.73
  104568019
  08/01/2024
  NASDAQ
  Common
  03/15/2024
  Restricted Stock Vesting
  Issuer
  N
  7300
  03/15/2024
  Compensation
  Y
  08/01/2024
  /s/ Daniel Tucci, as a duly authorized representative of Fidelity Brokerage Services LLC, as attorney-in-fact for Kevin Riley