When the first counties were created by the Kansas legislature in 1855, the territory within the present limits of the county was attached to Riley County for all revenue and judicial purposes.
1855年にカンザス準州議会が最初の郡を創設したとき、現在のクレイ郡にある領域は全ての歳入と司法権の目的でライリー郡に付設された。