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

    <schemaVersion>X0306</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2016-02-19</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0000101199</issuerCik>
        <issuerName>UNITED FIRE GROUP INC</issuerName>
        <issuerTradingSymbol>UFCS</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001451189</rptOwnerCik>
            <rptOwnerName>ERNST BARRIE W</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>118 2ND AVE SE</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>CEDAR RAPIDS</rptOwnerCity>
            <rptOwnerState>IA</rptOwnerState>
            <rptOwnerZipCode>52401-1212</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>1</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle>VP/Chief Investment Officer</officerTitle>
            <otherText></otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2016-02-19</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
                <footnoteId id="F1"/>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>2382</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>39.91</value>
                    <footnoteId id="F2"/>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>13790</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <derivativeTable>
        <derivativeTransaction>
            <securityTitle>
                <value>Stock Option (right to buy)</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <value>39.91</value>
            </conversionOrExercisePrice>
            <transactionDate>
                <value>2016-02-19</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>11286</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>39.91</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <exerciseDate>
                <footnoteId id="F3"/>
            </exerciseDate>
            <expirationDate>
                <value>2026-02-19</value>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>11286.0</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>11286</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </derivativeTransaction>
    </derivativeTable>

    <footnotes>
        <footnote id="F1">This transaction represents a grant of restricted stock shares to the Reporting Person under the Issuer's Stock Plan.</footnote>
        <footnote id="F2">The price per share is the closing price of the Issuer's common stock on the date of the reported transaction.</footnote>
        <footnote id="F3">Options become vested and exercisable in equal installments on 02/19/2017, 02/19/2018, 02/19/2019, 02/19/2020 and 02/19/2021, respectively.</footnote>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>/s/ Barrie W. Ernst by Michael T. Wilkins, Attorney-in-Fact</signatureName>
        <signatureDate>2016-02-23</signatureDate>
    </ownerSignature>
</ownershipDocument>
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X0306
4
2016-02-19
0
0000101199
UNITED FIRE GROUP INC
UFCS
0001451189
ERNST BARRIE W
118 2ND AVE SE
CEDAR RAPIDS
IA
52401-1212
0
1
0
0
VP/Chief Investment Officer
Common Stock
2016-02-19
4
A
0
2382
39.91
A
13790
D
Stock Option (right to buy)
39.91
2016-02-19
4
A
0
11286
39.91
A
2026-02-19
Common Stock
11286.0
11286
D
This transaction represents a grant of restricted stock shares to the Reporting Person under the Issuer's Stock Plan.
The price per share is the closing price of the Issuer's common stock on the date of the reported transaction.
Options become vested and exercisable in equal installments on 02/19/2017, 02/19/2018, 02/19/2019, 02/19/2020 and 02/19/2021, respectively.
/s/ Barrie W. Ernst by Michael T. Wilkins, Attorney-in-Fact
2016-02-23