Jefferson -- U.S. County in Montana Population (2000): 10049 Housing Units (2000): 4199 Land area (2000): 1656.636326 sq. miles (4290.668205 sq. km) Water area (2000): 2.193259 sq. miles (5.680515 sq. km) Total area (2000): 1658.829585 sq. miles (4296.348720 sq. km) Located within: Montana (MT), FIPS 30 Location: 46.119657 N, 112.117726 W Headwords: Jefferson Jefferson, MT Jefferson County Jefferson County, MT