<SEC-DOCUMENT>0001020569-18-000058.txt : 20180514
<SEC-HEADER>0001020569-18-000058.hdr.sgml : 20180514
<ACCEPTANCE-DATETIME>20180514180204
ACCESSION NUMBER:		0001020569-18-000058
CONFORMED SUBMISSION TYPE:	4
PUBLIC DOCUMENT COUNT:		1
CONFORMED PERIOD OF REPORT:	20180510
FILED AS OF DATE:		20180514
DATE AS OF CHANGE:		20180514

REPORTING-OWNER:	

	OWNER DATA:	
		COMPANY CONFORMED NAME:			DAUTEN KENT P
		CENTRAL INDEX KEY:			0001049128

	FILING VALUES:
		FORM TYPE:		4
		SEC ACT:		1934 Act
		SEC FILE NUMBER:	001-13045
		FILM NUMBER:		18832259

	MAIL ADDRESS:	
		STREET 1:		KEYSTONE CAPITAL INC
		STREET 2:		520 LAKE COOK ROAD SUITE 450
		CITY:			DEERFIELD
		STATE:			IL
		ZIP:			60015

ISSUER:		

	COMPANY DATA:	
		COMPANY CONFORMED NAME:			IRON MOUNTAIN INC
		CENTRAL INDEX KEY:			0001020569
		STANDARD INDUSTRIAL CLASSIFICATION:	REAL ESTATE INVESTMENT TRUSTS [6798]
		IRS NUMBER:				232588479
		STATE OF INCORPORATION:			DE
		FISCAL YEAR END:			1231

	BUSINESS ADDRESS:	
		STREET 1:		ONE FEDERAL STREET
		CITY:			BOSTON
		STATE:			MA
		ZIP:			02110
		BUSINESS PHONE:		617-535-4781

	MAIL ADDRESS:	
		STREET 1:		ONE FEDERAL STREET
		CITY:			BOSTON
		STATE:			MA
		ZIP:			02110

	FORMER COMPANY:	
		FORMER CONFORMED NAME:	IRON MOUNTAIN INC/PA
		DATE OF NAME CHANGE:	20000201

	FORMER COMPANY:	
		FORMER CONFORMED NAME:	PIERCE LEAHY CORP
		DATE OF NAME CHANGE:	19960807
</SEC-HEADER>
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<TYPE>4
<SEQUENCE>1
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<DESCRIPTION>FORM 4
<TEXT>
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    <issuer>
        <issuerCik>0001020569</issuerCik>
        <issuerName>IRON MOUNTAIN INC</issuerName>
        <issuerTradingSymbol>IRM</issuerTradingSymbol>
    </issuer>

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            <rptOwnerCik>0001049128</rptOwnerCik>
            <rptOwnerName>DAUTEN KENT P</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>C/O KEYSTONE CAPITAL, INC.</rptOwnerStreet1>
            <rptOwnerStreet2>155 NORTH WACKER DR. SUITE 4150</rptOwnerStreet2>
            <rptOwnerCity>CHICAGO</rptOwnerCity>
            <rptOwnerState>IL</rptOwnerState>
            <rptOwnerZipCode>60606</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle></officerTitle>
            <otherText></otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
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            <securityTitle>
                <value>Common Stock, par value $.01 per share</value>
            </securityTitle>
            <transactionDate>
                <value>2018-05-10</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>M</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>9261</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>24.902</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>2021938</value>
                </sharesOwnedFollowingTransaction>
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            <ownershipNature>
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        <nonDerivativeTransaction>
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                <value>Common Stock, par value $.01 per share</value>
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            <transactionDate>
                <value>2018-05-10</value>
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                <transactionFormType>4</transactionFormType>
                <transactionCode>M</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
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            <transactionAmounts>
                <transactionShares>
                    <value>9108</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>23.033</value>
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                <transactionAcquiredDisposedCode>
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                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>2031046</value>
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            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
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        <nonDerivativeTransaction>
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                <value>Common Stock, par value $.01 per share</value>
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            <transactionDate>
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    <derivativeTable>
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            <securityTitle>
                <value>Employee Stock Option (Right to Buy)</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <value>24.902</value>
            </conversionOrExercisePrice>
            <transactionDate>
                <value>2018-05-10</value>
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                <transactionPricePerShare>
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                <transactionAcquiredDisposedCode>
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            <exerciseDate>
                <footnoteId id="F1"/>
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            <expirationDate>
                <value>2018-06-05</value>
            </expirationDate>
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                <underlyingSecurityTitle>
                    <value>Common Stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>9261.0</value>
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                    <value>0</value>
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            </securityTitle>
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                <value>23.033</value>
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                <value>2018-05-10</value>
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                <transactionFormType>4</transactionFormType>
                <transactionCode>M</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
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                <transactionShares>
                    <value>9108</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0</value>
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                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
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            <exerciseDate>
                <footnoteId id="F2"/>
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            <expirationDate>
                <value>2019-06-04</value>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>9108.0</value>
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                    <value>0</value>
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                    <value>D</value>
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                <value>Employee Stock Option (Right to Buy)</value>
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            <conversionOrExercisePrice>
                <value>19.251</value>
            </conversionOrExercisePrice>
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                <value>2018-05-10</value>
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                <transactionCode>M</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
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                <transactionShares>
                    <value>15555</value>
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                <transactionPricePerShare>
                    <value>0</value>
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                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
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            <exerciseDate>
                <footnoteId id="F3"/>
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            <expirationDate>
                <value>2020-06-04</value>
            </expirationDate>
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                    <value>0</value>
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    </derivativeTable>

    <footnotes>
        <footnote id="F1">This stock option, representing a right to purchase a total of 9,261 shares, is fully vested. The number of stock options granted includes previously reported adjustments effective on September 26, 2014 made in connection with the special distribution declared by the Board of Directors of the Issuer on September 15, 2014 and paid on November 4, 2014 (the &quot;Special Distribution&quot;).</footnote>
        <footnote id="F2">This stock option, representing a right to purchase a total of 9,108 shares, is fully vested. The number of stock options granted includes previously reported adjustments effective on September 26, 2014 made in connection with the Special Distribution.</footnote>
        <footnote id="F3">This stock option, representing a right to purchase a total of 15,555 shares, is fully vested. The number of stock options granted includes previously reported adjustments effective on September 26, 2014 made in connection with the Special Distribution.</footnote>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>/s/ Elizabeth Tammaro, under Power of Attorney dated May 26, 2016, from Kent P. Dauten</signatureName>
        <signatureDate>2018-05-14</signatureDate>
    </ownerSignature>
</ownershipDocument>
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</TEXT>
</DOCUMENT>
</SEC-DOCUMENT>
