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

    <schemaVersion>X0202</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2007-06-20</periodOfReport>

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

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001140106</rptOwnerCik>
            <rptOwnerName>COHEN ERIC I</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>TEREX CORPORATION</rptOwnerStreet1>
            <rptOwnerStreet2>200 NYALA FARM ROAD</rptOwnerStreet2>
            <rptOwnerCity>WESTPORT</rptOwnerCity>
            <rptOwnerState>CT</rptOwnerState>
            <rptOwnerZipCode>06880</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>1</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle>Senior V.P., Secy. Gen Counsel</officerTitle>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock, par value $.01</value>
            </securityTitle>
            <transactionDate>
                <value>2007-06-20</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>S</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>10000</value>
                    <footnoteId id="F1"/>
                </transactionShares>
                <transactionPricePerShare>
                    <value>84.92</value>
                    <footnoteId id="F2"/>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>99819</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value></value>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock, par value $.01</value>
            </securityTitle>
            <transactionDate>
                <value>2007-06-20</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>5</transactionFormType>
                <transactionCode>G</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>1165</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>98654</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value></value>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock, par value $.01</value>
            </securityTitle>
            <transactionDate>
                <value>2007-06-20</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>5</transactionFormType>
                <transactionCode>I</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>0</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>1200</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>By children</value>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock, par value $.01</value>
            </securityTitle>
            <transactionDate>
                <value>2007-06-20</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>5</transactionFormType>
                <transactionCode>I</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>0</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>4501</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>401(k) plan</value>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <footnotes>
        <footnote id="F1">Transaction executed pursuant to a Rule 10b5-1 stock trading plan.</footnote>
        <footnote id="F2">Represents average sale price.  Shares sold at various prices ranging from $84.28 to $86.17 as follows: 200 @ $84.28; 500 @ $84.29; 600 @ $84.34; 100 @ $84.35; 100 @ $84.49; 200 @ $84.52; 200 @ $84.56; 100 @ $84.57; 200 @ $84.60; 300 @ $84.63; 200 @ $84.64; 100 @ $84.65; 100 @ $84.67; 200 @ $84.68; 100 @ $84.73; 100 @ $84.77; 100 @ $84.78; 400 @ $84.80; 200 @ $84.82; 100 @ $84.84; 200 @ $84.85; 100 @ $84.87; 400 @ $84.90; 900 @ $84.94; 400 @ $84.95; 200 @ $84.98; 300 @ $84.99; 300 @ $85.01; 100 @ $85.02; 100 @ $85.10; 200 @ $85.18; 100 @ $85.20; 100 @ $85.25; 900 @ $85.33; 800 @ $85.37; 300 @ $85.44; 100 @ $85.48; 100 @ $85.53; 200 @ $85.60 and 100 @ $86.17.</footnote>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>/s/ Eric I Cohen</signatureName>
        <signatureDate>2007-06-21</signatureDate>
    </ownerSignature>
</ownershipDocument>
[{"type": "4", "sequence": "1", "filename": "edgar.xml", "description": "PRIMARY DOCUMENT", "secsgml_size_bytes": 8390}]
X0202
4
2007-06-20
0000097216
TEREX CORP
TEX
0001140106
COHEN ERIC I
TEREX CORPORATION
200 NYALA FARM ROAD
WESTPORT
CT
06880
0
1
0
0
Senior V.P., Secy. Gen Counsel
Common Stock, par value $.01
2007-06-20
4
S
0
10000
84.92
D
99819
D
Common Stock, par value $.01
2007-06-20
5
G
0
1165
0
D
98654
D
Common Stock, par value $.01
2007-06-20
5
I
0
0
0
A
1200
I
By children
Common Stock, par value $.01
2007-06-20
5
I
0
0
0
A
4501
I
401(k) plan
Transaction executed pursuant to a Rule 10b5-1 stock trading plan.
Represents average sale price.  Shares sold at various prices ranging from $84.28 to $86.17 as follows: 200 @ $84.28; 500 @ $84.29; 600 @ $84.34; 100 @ $84.35; 100 @ $84.49; 200 @ $84.52; 200 @ $84.56; 100 @ $84.57; 200 @ $84.60; 300 @ $84.63; 200 @ $84.64; 100 @ $84.65; 100 @ $84.67; 200 @ $84.68; 100 @ $84.73; 100 @ $84.77; 100 @ $84.78; 400 @ $84.80; 200 @ $84.82; 100 @ $84.84; 200 @ $84.85; 100 @ $84.87; 400 @ $84.90; 900 @ $84.94; 400 @ $84.95; 200 @ $84.98; 300 @ $84.99; 300 @ $85.01; 100 @ $85.02; 100 @ $85.10; 200 @ $85.18; 100 @ $85.20; 100 @ $85.25; 900 @ $85.33; 800 @ $85.37; 300 @ $85.44; 100 @ $85.48; 100 @ $85.53; 200 @ $85.60 and 100 @ $86.17.
/s/ Eric I Cohen
2007-06-21