<?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>0001515002</rptOwnerCik>
            <rptOwnerName>Sheeley Michael J.</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/COO - United Life Ins. Co.</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>1435</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>39.91</value>
                    <footnoteId id="F2"/>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>6999</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>6799</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>6799.0</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>6799</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/ Michael J. Sheeley 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
0001515002
Sheeley Michael J.
118 2ND AVE SE
CEDAR RAPIDS
IA
52401-1212
0
1
0
0
VP/COO - United Life Ins. Co.
Common Stock
2016-02-19
4
A
0
1435
39.91
A
6999
D
Stock Option (right to buy)
39.91
2016-02-19
4
A
0
6799
39.91
A
2026-02-19
Common Stock
6799.0
6799
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/ Michael J. Sheeley by Michael T. Wilkins, Attorney-in-Fact
2016-02-23