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

    <schemaVersion>X0306</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2017-04-05</periodOfReport>

    <issuer>
        <issuerCik>0000097216</issuerCik>
        <issuerName>TEREX CORP</issuerName>
        <issuerTradingSymbol>TEX</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001697487</rptOwnerCik>
            <rptOwnerName>HEPLER MATTHEW</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>C/O TEREX CORPORATION</rptOwnerStreet1>
            <rptOwnerStreet2>200 NYALA FARM ROAD</rptOwnerStreet2>
            <rptOwnerCity>WESTPORT</rptOwnerCity>
            <rptOwnerState>CT</rptOwnerState>
            <rptOwnerZipCode>06880</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock, par value $.01</value>
            </securityTitle>
            <transactionDate>
                <value>2017-04-05</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>1130</value>
                    <footnoteId id="F1"/>
                </transactionShares>
                <transactionPricePerShare>
                    <value>31.75</value>
                    <footnoteId id="F2"/>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>1130</value>
                    <footnoteId id="F3"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value></value>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <footnotes>
        <footnote id="F1">Represents prorata payment of annual director retainer.</footnote>
        <footnote id="F2">Price set in accordance with the terms of the Company's outside director compensation program.</footnote>
        <footnote id="F3">The reporting person disclaims beneficial ownership of the shares of and derivatives related to the common stock of the Issuer as reported as beneficially owned by Marcato Capital Management LP, Marcato International Master Fund, Ltd., and Richard T. McGuire III, and accordingly this report does not include such shares and derivatives.</footnote>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>/s/Scott J. Posner, by power of attorney</signatureName>
        <signatureDate>2017-04-06</signatureDate>
    </ownerSignature>
</ownershipDocument>
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X0306
4
2017-04-05
0000097216
TEREX CORP
TEX
0001697487
HEPLER MATTHEW
C/O TEREX CORPORATION
200 NYALA FARM ROAD
WESTPORT
CT
06880
1
0
0
0
Common Stock, par value $.01
2017-04-05
4
A
0
1130
31.75
A
1130
D
Represents prorata payment of annual director retainer.
Price set in accordance with the terms of the Company's outside director compensation program.
The reporting person disclaims beneficial ownership of the shares of and derivatives related to the common stock of the Issuer as reported as beneficially owned by Marcato Capital Management LP, Marcato International Master Fund, Ltd., and Richard T. McGuire III, and accordingly this report does not include such shares and derivatives.
/s/Scott J. Posner, by power of attorney
2017-04-06