Macomb is a city in and the county seat of McDonough County, Illinois, United States. It is situated in western Illinois southwest of Galesburg. Macomb is the home of Western Illinois University. According to the United States Census Bureau, the city has a total area of 10.2 square miles (26km2). 9.9 square miles (26km2) of it is land and 0.4 square miles (1.0km2) of it (3.90%) is water.