McDonough County is a county in the U.S. state of Illinois. According to the 2020 census, it had a population of 27,238. Its county seat is Macomb, which is also the home of Western Illinois University.

Macomb is a city in and the county seat of McDonough County, Illinois, United States. It is situated in western Illinois, about 75 miles (121 km) southwest of Peoria. As of the 2020 census the population of the city was 15,051, down from 19,288 in 2010. Macomb is the home of Western Illinois University.