Greene County, Illinois

Greene County, Illinois
Greene County Courthouse
Location within the U.S. state of Illinois
Coordinates: 39°21′N 90°23′W / 39.35°N 90.39°W / 39.35; -90.39
Country United States
State Illinois
Founded1821
Named afterNathanael Greene
SeatCarrollton
Largest cityCarrollton
Area
 • Total
546 sq mi (1,410 km2)
 • Land543 sq mi (1,410 km2)
 • Water3.3 sq mi (8.5 km2)  0.6%
Population
 (2020)
 • Total
11,985
 • Estimate 
(2024)
11,417
 • Density22.1/sq mi (8.52/km2)
Time zoneUTC−6 (Central)
 • Summer (DST)UTC−5 (CDT)
Congressional district15th

Greene County is a county located in the U.S. state of Illinois. According to the 2020 United States census, it has a population of 11,843. Its county seat is Carrollton.

A notable archaeological area, the Koster Site, has produced evidence of more than 7,000 years of human habitation. Artifacts from the site are displayed at the Center for American Archeology in Kampsville, Illinois.