<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0508</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2026-01-20</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0001409493</issuerCik>
        <issuerName>CHIMERA INVESTMENT CORP</issuerName>
        <issuerTradingSymbol>CIM</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001652530</rptOwnerCik>
            <rptOwnerName>Kardis Phillip John II</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>C/O: CHIMERA INVESTMENT CORPORATION</rptOwnerStreet1>
            <rptOwnerStreet2>630 FIFTH AVENUE, SUITE 2400</rptOwnerStreet2>
            <rptOwnerCity>NEW YORK</rptOwnerCity>
            <rptOwnerState>NY</rptOwnerState>
            <rptOwnerZipCode>10111</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
            <isOfficer>1</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle>President and CEO</officerTitle>
        </reportingOwnerRelationship>
    </reportingOwner>

    <aff10b5One>0</aff10b5One>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2026-01-20</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>194774</value>
                    <footnoteId id="F1"/>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0</value>
                    <footnoteId id="F2"/>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>695495</value>
                    <footnoteId id="F3"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <derivativeTable></derivativeTable>

    <footnotes>
        <footnote id="F1">Represents shares of Chimera Investment Corporation (&quot;Chimera&quot;) common stock underlying restricted stock units (&quot;RSUs&quot;). The RSUs are scheduled to vest one-third per year on December 31st of 2026, 2027 and 2028 and shall be settled 100% in shares of Chimera common stock. The reporting person does not intend to report the vesting of the RSUs nor the delivery of the shares of common stock.</footnote>
        <footnote id="F2">Each RSU is the economic equivalent of one share of Chimera common stock.</footnote>
        <footnote id="F3">Dividend equivalent rights (&quot;DERs&quot;) issued on RSUs and underlying performance stock units or PSUs are included in the reporting person's common stock holding balance. Each DER is the economic equivalent of one share of Chimera common stock.</footnote>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>/s/ Phillip John Kardis II</signatureName>
        <signatureDate>2026-01-21</signatureDate>
    </ownerSignature>
</ownershipDocument>
