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

    <schemaVersion>X0306</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2014-09-15</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

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

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001023710</rptOwnerCik>
            <rptOwnerName>MILLIGAN GEORGE D</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>118 SECOND AVENUE SE</rptOwnerStreet1>
            <rptOwnerStreet2>P.O. BOX 73909</rptOwnerStreet2>
            <rptOwnerCity>CEDAR RAPIDS</rptOwnerCity>
            <rptOwnerState>IA</rptOwnerState>
            <rptOwnerZipCode>52407-3909</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle></officerTitle>
            <otherText></otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2014-09-15</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>5</transactionFormType>
                <transactionCode>J</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
                <footnoteId id="F1"/>
            </transactionCoding>
            <transactionTimeliness>
                <value>E</value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>18</value>
                    <footnoteId id="F2"/>
                </transactionShares>
                <transactionPricePerShare>
                    <value>28.5213</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>15567</value>
                    <footnoteId id="F3"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <derivativeTable></derivativeTable>

    <footnotes>
        <footnote id="F1">Shares acquired through participation in the Issuer's Dividend Reinvestment Plan.</footnote>
        <footnote id="F2">Represents the approximate number of shares (excluding fractionals) acquired by the Reporting Person through the Issuer's Dividend Reinvestment Plan.</footnote>
        <footnote id="F3">The number of shares beneficially held directly by the Reporting Person (excluding fractionals) following the reported transaction includes: 12,942 shares held by Mr. Milligan in separate brokerge accounts; 1,339 shares held of record by Mr. Milligan; and 1,286 shares of restricted stock which vest, subject to certain conditions, on May 21, 2017.</footnote>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>/s/ George D. Milligan by Dianne M. Lyons, Attorney-in-Fact</signatureName>
        <signatureDate>2014-09-19</signatureDate>
    </ownerSignature>
</ownershipDocument>
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X0306
4
2014-09-15
0
0000101199
UNITED FIRE GROUP INC
UFCS
0001023710
MILLIGAN GEORGE D
118 SECOND AVENUE SE
P.O. BOX 73909
CEDAR RAPIDS
IA
52407-3909
1
0
0
0
Common Stock
2014-09-15
5
J
0
E
18
28.5213
A
15567
D
Shares acquired through participation in the Issuer's Dividend Reinvestment Plan.
Represents the approximate number of shares (excluding fractionals) acquired by the Reporting Person through the Issuer's Dividend Reinvestment Plan.
The number of shares beneficially held directly by the Reporting Person (excluding fractionals) following the reported transaction includes: 12,942 shares held by Mr. Milligan in separate brokerge accounts; 1,339 shares held of record by Mr. Milligan; and 1,286 shares of restricted stock which vest, subject to certain conditions, on May 21, 2017.
/s/ George D. Milligan by Dianne M. Lyons, Attorney-in-Fact
2014-09-19