<SEC-DOCUMENT>0000860413-23-000145.txt : 20230605
<SEC-HEADER>0000860413-23-000145.hdr.sgml : 20230605
<ACCEPTANCE-DATETIME>20230605124509
ACCESSION NUMBER:		0000860413-23-000145
CONFORMED SUBMISSION TYPE:	4
PUBLIC DOCUMENT COUNT:		1
CONFORMED PERIOD OF REPORT:	20230601
FILED AS OF DATE:		20230605
DATE AS OF CHANGE:		20230605

REPORTING-OWNER:	

	OWNER DATA:	
		COMPANY CONFORMED NAME:			HENNING THOMAS EDWARD
		CENTRAL INDEX KEY:			0001269806

	FILING VALUES:
		FORM TYPE:		4
		SEC ACT:		1934 Act
		SEC FILE NUMBER:	001-34653
		FILM NUMBER:		23991748

	MAIL ADDRESS:	
		STREET 1:		121 SOUTH 13TH STREET
		STREET 2:		SUITE 100
		CITY:			LINCOLN
		STATE:			NE
		ZIP:			68508

ISSUER:		

	COMPANY DATA:	
		COMPANY CONFORMED NAME:			FIRST INTERSTATE BANCSYSTEM INC
		CENTRAL INDEX KEY:			0000860413
		STANDARD INDUSTRIAL CLASSIFICATION:	STATE COMMERCIAL BANKS [6022]
		IRS NUMBER:				810331430
		STATE OF INCORPORATION:			DE
		FISCAL YEAR END:			1231

	BUSINESS ADDRESS:	
		STREET 1:		401 NO 31ST STREET
		CITY:			BILLINGS
		STATE:			MT
		ZIP:			59101
		BUSINESS PHONE:		4062555311

	MAIL ADDRESS:	
		STREET 1:		401 NO 31ST STREET
		CITY:			BILLINGS
		STATE:			MT
		ZIP:			59101

	FORMER COMPANY:	
		FORMER CONFORMED NAME:	FIRST INTERSTATE BANCSYSTEM OF MONTANA INC
		DATE OF NAME CHANGE:	19930615
</SEC-HEADER>
<DOCUMENT>
<TYPE>4
<SEQUENCE>1
<FILENAME>wf-form4_168598349730464.xml
<DESCRIPTION>FORM 4
<TEXT>
<XML>
<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0407</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2023-06-01</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0000860413</issuerCik>
        <issuerName>FIRST INTERSTATE BANCSYSTEM INC</issuerName>
        <issuerTradingSymbol>FIBK</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001269806</rptOwnerCik>
            <rptOwnerName>HENNING THOMAS EDWARD</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>6015 THE KNOLLS</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>LINCOLN</rptOwnerCity>
            <rptOwnerState>NE</rptOwnerState>
            <rptOwnerZipCode>68512</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle></officerTitle>
            <otherText></otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <aff10b5One>0</aff10b5One>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Class A Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2023-06-01</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>3401</value>
                    <footnoteId id="F1"/>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>24052</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <derivativeTable></derivativeTable>

    <footnotes>
        <footnote id="F1">Shares issuable upon vesting of restricted stock units granted to the reporting person pursuant to the Registrant's 2023 Equity and Incentive Plan. The restricted stock units vest on June 1, 2024, subject to the reporting persons provision of continuous service to the Registrant through the vesting date.</footnote>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>/s/ Kirk D. Jensen, Attorney-in-Fact for Reporting Person</signatureName>
        <signatureDate>2023-06-01</signatureDate>
    </ownerSignature>
</ownershipDocument>
</XML>
</TEXT>
</DOCUMENT>
</SEC-DOCUMENT>
