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.

U.S. Route 136 is an east-west U.S. highway that is a spur route of U.S. Route 36. It runs from Edison, Nebraska, at U.S. Route 6 and U.S. Route 34 to the Interstate 74/Interstate 465 interchange in Speedway, Indiana. This is a distance of 804 miles (1,294 km). Due to the removal of almost every numbered route in Indianapolis, US 136 never meets its parent, US 36; however, it does come within two miles of it at its interchange with I-465/I-74 at its eastern terminus.