Jefferson -- U.S. County in Idaho Population (2000): 19155 Housing Units (2000): 6287 Land area (2000): 1095.083261 sq. miles (2836.252504 sq. km) Water area (2000): 10.469638 sq. miles (27.116238 sq. km) Total area (2000): 1105.552899 sq. miles (2863.368742 sq. km) Located within: Idaho (ID), FIPS 16 Location: 43.761293 N, 112.106831 W Headwords: Jefferson Jefferson, ID Jefferson County Jefferson County, ID