'Jefferson County, IL' definitions:
Jefferson -- U.S. County in Illinois
From: Gazetteer 2000
Name :
Jefferson -- U.S. County in Illinois
Population (2000) :
40045
Housing Units (2000) :
16990
Land area (2000) :
570.955719 sq. miles (1478.768461 sq. km)
Water area (2000) :
12.757198 sq. miles (33.040991 sq. km)
Total area (2000) :
583.712917 sq. miles (1511.809452 sq. km)
Located within :
Illinois (IL), FIPS 17
Location :
38.310378 N, 88.915252 W