Jefferson -- U.S. County in Iowa Population (2000): 16181 Housing Units (2000): 7241 Land area (2000): 435.340811 sq. miles (1127.527476 sq. km) Water area (2000): 1.376020 sq. miles (3.563874 sq. km) Total area (2000): 436.716831 sq. miles (1131.091350 sq. km) Located within: Iowa (IA), FIPS 19 Location: 41.031640 N, 91.963376 W Headwords: Jefferson Jefferson, IA Jefferson County Jefferson County, IA