Marshall County, Illinois

Marshall County
Lacon Bridge in the county seat
Location within the U.S. state of Illinois
Illinois's location within the U.S.
Coordinates: 41°02′N 89°20′W / 41.03°N 89.34°W / 41.03; -89.34
Country United States
State Illinois
FoundedJanuary 19, 1839
Named afterJohn Marshall
SeatLacon
Largest cityHenry
Area
  Total
399 sq mi (1,030 km2)
  Land387 sq mi (1,000 km2)
  Water12 sq mi (30 km2)  2.9%
Population
 (2020)
  Total
11,742
  Estimate 
(2023)
11,683
  Density29/sq mi (11/km2)
Time zoneUTC−6 (Central)
  Summer (DST)UTC−5 (CDT)
Congressional district16th
Websitewww.marshallcountyillinois.com

Marshall County is a county located in the U.S. state of Illinois. According to the 2020 census, it had a population of 11,742. Its county seat is Lacon. Marshall County is part of the Peoria metropolitan area.