    <SEC-DOCUMENT>0000860413-18-000157-index.html : 20181011
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    <ACCEPTANCE-DATETIME>20181011163457
    ACCESSION NUMBER:		0000860413-18-000157
    CONFORMED SUBMISSION TYPE:	8-K
    PUBLIC DOCUMENT COUNT:		18
    CONFORMED PERIOD OF REPORT:	20181011
    ITEM INFORMATION:		Entry into a Material Definitive Agreement
    ITEM INFORMATION:		Other Events
    ITEM INFORMATION:		Financial Statements and Exhibits
    FILED AS OF DATE:		20181011
    DATE AS OF CHANGE:		20181011

    FILER:

    	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:			MT
    		FISCAL YEAR END:			1231

    	FILING VALUES:
    		FORM TYPE:		8-K
    		SEC ACT:		1934 Act
    		SEC FILE NUMBER:	001-34653
    		FILM NUMBER:		181118642

    	BUSINESS ADDRESS:
    		STREET 1:		P O BOX 30918
    		STREET 2:		401 NO 31ST STREET
    		CITY:			BILLINGS
    		STATE:			MT
    		ZIP:			59116-0918
    		BUSINESS PHONE:		4062555300

    	MAIL ADDRESS:
    		STREET 1:		P O BOX 30918
    		STREET 2:		401 NO 31ST STREET
    		CITY:			BILLINGS
    		STATE:			MT
    		ZIP:			59116-0918

    	FORMER COMPANY:
    		FORMER CONFORMED NAME:	FIRST INTERSTATE BANCSYSTEM OF MONTANA INC
    		DATE OF NAME CHANGE:	19930615
    </SEC-HEADER>
    <DOCUMENT>
    <TYPE>8-K
    <SEQUENCE>1
    <FILENAME>fibk20181011-8kcmyf.htm
    <DESCRIPTION>8-K
    <TEXT>
    Document 1 - file: fibk20181011-8kcmyf.htm

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    <FILENAME>ex-21cmyfmergeragmt.htm
    <DESCRIPTION>EX-2.1
    <TEXT>
    Document 2 - file: ex-21cmyfmergeragmt.htm

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    <FILENAME>ex991ip.htm
    <DESCRIPTION>EX-99.1
    <TEXT>
    Document 3 - file: ex991ip.htm

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    <DESCRIPTION>EX-99.2
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    Document 4 - file: ex-992xjointpr.htm

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    <FILENAME>ex991ip001.jpg
    <DESCRIPTION>GRAPHIC
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    Document 5 - file: ex991ip001.jpg

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    <FILENAME>ex991ip002.jpg
    <DESCRIPTION>GRAPHIC
    <TEXT>
    Document 6 - file: ex991ip002.jpg

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    <SEQUENCE>7
    <FILENAME>ex991ip003.jpg
    <DESCRIPTION>GRAPHIC
    <TEXT>
    Document 7 - file: ex991ip003.jpg

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    Document 8 - file: ex991ip004.jpg

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    Document 9 - file: ex991ip005.jpg

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    <DESCRIPTION>GRAPHIC
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    Document 10 - file: ex991ip006.jpg

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    Document 11 - file: ex991ip007.jpg

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    <FILENAME>ex991ip008.jpg
    <DESCRIPTION>GRAPHIC
    <TEXT>
    Document 12 - file: ex991ip008.jpg

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    <FILENAME>ex991ip009.jpg
    <DESCRIPTION>GRAPHIC
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    Document 13 - file: ex991ip009.jpg

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    Document 14 - file: ex991ip010.jpg

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    Document 15 - file: ex991ip011.jpg

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    <DESCRIPTION>GRAPHIC
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    Document 16 - file: ex991ip012.jpg

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    <SEQUENCE>17
    <FILENAME>ex991ip013.jpg
    <DESCRIPTION>GRAPHIC
    <TEXT>
    Document 17 - file: ex991ip013.jpg

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    Document 18 - file: ex991ip014.jpg

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