Jefferson -- U.S. County in Missouri Population (2000): 198099 Housing Units (2000): 75586 Land area (2000): 656.796138 sq. miles (1701.094116 sq. km) Water area (2000): 7.290396 sq. miles (18.882037 sq. km) Total area (2000): 664.086534 sq. miles (1719.976153 sq. km) Located within: Missouri (MO), FIPS 29 Location: 38.285842 N, 90.499266 W Headwords: Jefferson Jefferson, MO Jefferson County Jefferson County, MO