'Lake County, IL' definitions:

Lake -- U.S. County in Illinois

From: Gazetteer 2000
Name :
Lake -- U.S. County in Illinois
Population (2000) :
644356
Housing Units (2000) :
225919
Land area (2000) :
447.563704 sq. miles (1159.184623 sq. km)
Water area (2000) :
920.386660 sq. miles (2383.790404 sq. km)
Total area (2000) :
1367.950364 sq. miles (3542.975027 sq. km)
Located within :
Illinois (IL), FIPS 17
Location :
42.313322 N, 87.983801 W