Jefferson -- U.S. County in Mississippi Population (2000): 9740 Housing Units (2000): 3819 Land area (2000): 519.387161 sq. miles (1345.206514 sq. km) Water area (2000): 7.805469 sq. miles (20.216072 sq. km) Total area (2000): 527.192630 sq. miles (1365.422586 sq. km) Located within: Mississippi (MS), FIPS 28 Location: 31.739326 N, 91.046970 W Headwords: Jefferson Jefferson, MS Jefferson County Jefferson County, MS