Marion County, Illinois

Marion County, Illinois
Location within the U.S. state of Illinois
Coordinates: 38°39′N 88°55′W / 38.65°N 88.92°W / 38.65; -88.92
Country United States
State Illinois
Founded1823
Named afterFrancis Marion
SeatSalem
Largest cityCentralia
Area
 • Total
576 sq mi (1,490 km2)
 • Land572 sq mi (1,480 km2)
 • Water3.7 sq mi (9.6 km2)  0.6%
Population
 (2020)
 • Total
37,729
 • Estimate 
(2024)
36,437
 • Density66.0/sq mi (25.5/km2)
Time zoneUTC−6 (Central)
 • Summer (DST)UTC−5 (CDT)
Congressional district15th

Marion County is a county located in the U.S. state of Illinois. According to the 2020 census, it had a population of 37,729. Its county seat is Salem. Marion County comprises the Centralia, IL Micropolitan Statistical Area, which is included in the St. Louis-St. Charles-Farmington, MO-IL Combined Statistical Area.