Lewistown is a city in Fulton County, Illinois, United States. It was named by its founder, Ossian M. Ross, for his oldest son, Lewis W. Ross. The population was 2,522 at the 2000 census. It is the county seat of Fulton County. Located in central Illinois, it is southwest of Peoria. It is the source of Spoon River Anthology by Edgar Lee Masters, who lived there.