<SEC-DOCUMENT>0001020569-23-000063.txt : 20230227
<SEC-HEADER>0001020569-23-000063.hdr.sgml : 20230227
<ACCEPTANCE-DATETIME>20230227181642
ACCESSION NUMBER:		0001020569-23-000063
CONFORMED SUBMISSION TYPE:	4
PUBLIC DOCUMENT COUNT:		1
CONFORMED PERIOD OF REPORT:	20230223
FILED AS OF DATE:		20230227
DATE AS OF CHANGE:		20230227

REPORTING-OWNER:	

	OWNER DATA:	
		COMPANY CONFORMED NAME:			McIntosh Greg W
		CENTRAL INDEX KEY:			0001769841

	FILING VALUES:
		FORM TYPE:		4
		SEC ACT:		1934 Act
		SEC FILE NUMBER:	001-13045
		FILM NUMBER:		23677208

	MAIL ADDRESS:	
		STREET 1:		C/O IRON MOUNTAIN INCORPORATED
		STREET 2:		ONE FEDERAL STREET
		CITY:			BOSTON
		STATE:			MA
		ZIP:			02110

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:		85 NEW HAMPSHIRE AVENUE, SUITE 150
		STREET 2:		PEASE INTERNATIONAL TRADEPORT
		CITY:			PORTSMOUTH
		STATE:			NH
		ZIP:			03801
		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>
<DOCUMENT>
<TYPE>4
<SEQUENCE>1
<FILENAME>wf-form4_167753977881570.xml
<DESCRIPTION>FORM 4
<TEXT>
<XML>
<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0306</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2023-02-23</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0001020569</issuerCik>
        <issuerName>IRON MOUNTAIN INC</issuerName>
        <issuerTradingSymbol>IRM</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001769841</rptOwnerCik>
            <rptOwnerName>McIntosh Greg W</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>C/O IRON MOUNTAIN INCORPORATED</rptOwnerStreet1>
            <rptOwnerStreet2>85 NEW HAMPSHIRE AVENUE, SUITE 150</rptOwnerStreet2>
            <rptOwnerCity>PORTSMOUTH</rptOwnerCity>
            <rptOwnerState>NH</rptOwnerState>
            <rptOwnerZipCode>03801</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>1</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle>EVP, CCO &amp; GM, Global RM</officerTitle>
            <otherText></otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock, par value $.01 per share</value>
            </securityTitle>
            <transactionDate>
                <value>2023-02-23</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>M</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>9618</value>
                    <footnoteId id="F1"/>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>16798</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock, par value $.01 per share</value>
            </securityTitle>
            <transactionDate>
                <value>2023-02-23</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>F</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>5148</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>52.77</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>11650</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <derivativeTable>
        <derivativeTransaction>
            <securityTitle>
                <value>Performance Units</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <footnoteId id="F2"/>
            </conversionOrExercisePrice>
            <transactionDate>
                <value>2023-02-23</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>9618</value>
                    <footnoteId id="F3"/>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <exerciseDate>
                <footnoteId id="F4"/>
            </exerciseDate>
            <expirationDate>
                <footnoteId id="F4"/>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>9618.0</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>9618</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </derivativeTransaction>
        <derivativeTransaction>
            <securityTitle>
                <value>Performance Units</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <footnoteId id="F2"/>
            </conversionOrExercisePrice>
            <transactionDate>
                <value>2023-02-23</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>M</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>9618</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <exerciseDate>
                <footnoteId id="F5"/>
            </exerciseDate>
            <expirationDate>
                <footnoteId id="F5"/>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>9618.0</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>0</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </derivativeTransaction>
    </derivativeTable>

    <footnotes>
        <footnote id="F1">This acquisition is reported to reflect the full vesting of performance units (&quot;PUs&quot;) previously granted to the Reporting Person on February 19, 2020. Effective February 23, 2023, the Compensation Committee of Iron Mountain Incorporated's Board of Directors (the &quot;Compensation Committee&quot;) determined the actual award of PUs under the grant after completion of the relevant performance period, and the PUs vested in full on February 23, 2023.</footnote>
        <footnote id="F2">Each PU represents a contingent right to receive one share of Iron Mountain Incorporated common stock (&quot;Common Stock&quot;).</footnote>
        <footnote id="F3">The PUs were initially granted to the Reporting Person on February 19, 2020. This Form 4 is being filed to reflect the determination by the Compensation Committee, effective as of February 23, 2023, of the actual award of PUs under the grant after completion of the relevant performance period.</footnote>
        <footnote id="F4">The PUs were initially granted to the Reporting Person on February 19, 2020 and fully vested on February 23, 2023.</footnote>
        <footnote id="F5">The PUs were initially granted to the Reporting Person on February 19, 2020. Effective February 23, 2023, the Compensation Committee determined the actual award of PUs under the grant after completion of the relevant performance period, and the PUs vested in full on February 23, 2023.</footnote>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>/s/ Elizabeth Tammaro, under Power of Attorney dated February 26, 2019 from Greg McIntosh</signatureName>
        <signatureDate>2023-02-27</signatureDate>
    </ownerSignature>
</ownershipDocument>
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</TEXT>
</DOCUMENT>
</SEC-DOCUMENT>
