Warren County, Illinois

Warren County
Warren County Courthouse in Monmouth
Location within the U.S. state of Illinois
Illinois's location within the U.S.
Coordinates: 40°51′N 90°37′W / 40.85°N 90.61°W / 40.85; -90.61
Country United States
State Illinois
Founded1825
Named afterJoseph Warren
SeatMonmouth
Largest cityMonmouth
Area
  Total
543 sq mi (1,410 km2)
  Land542 sq mi (1,400 km2)
  Water0.6 sq mi (2 km2)  0.1%
Population
 (2020)
  Total
16,835
  Estimate 
()
16,185
  Density31/sq mi (12/km2)
Time zoneUTC−6 (Central)
  Summer (DST)UTC−5 (CDT)
Congressional districts15th, 17th
Websitewww.warrencountyil.com

Warren County is a county in the U.S. state of Illinois. According to the 2020 census, it had a population of 16,835. Its county seat is Monmouth.