Macomb /məˈkoʊm/ is a city in and the county seat of McDonough County, Illinois, United States. It is situated in western Illinois, southwest of Galesburg. The city is about 75 miles southwest of Peoria and 77 miles south of the Quad Cities. A special census held in 2014 placed the city's population at 21,516. Macomb is the home of Western Illinois University.