Monmouth is a city in and the county seat of Warren County, Illinois, United States. The population was 9,444 at the 2010 census, down from 9,841 in 2000. It is the home of Monmouth College and contains Monmouth Park, Harmon Park, North Park, Warfield Park, West Park, South Park, Garwood Park, Buster White Park and the Citizens Lake & Campground. It is the host of the Prime Beef festival, held annually the week after Labor Day. The festival is kicked off with one of the largest parades in Western Illinois. Monmouth is also known regionally as the "Maple City". </ref>It is part of the Galesburg Micropolitan Statistical Area.
The town established in 1831 was originally going to be called Kosciusko (the name was drawn out of a hat), but the founders of the town feared that it would be difficult to spell and pronounce. The name 'Monmouth' was put forward by a resident who had lived in Monmouth County, New Jersey.
In 1841, Latter Day Saint movement founder Joseph Smith appeared before Judge Stephen A. Douglas in an extradition hearing held at Monmouth's Warren County courthouse. The hearing, which was to determine whether Smith should be returned to Missouri to face murder charges, resulted in freedom for the defendant, as it was determined that his arrest had been invalid.