Monroe is the largest city in Monroe County, Michigan, United States, and its county seat. The population was 20,462 at the 2020 census. The city is bordered on the south by Monroe Charter Township, but the two are administered autonomously. Monroe is the core city in the Monroe metropolitan area, which is coterminous with Monroe County and had a population of 154,809 in 2020. On the western shores of Lake Erie about 20 miles (32 km) northeast of Toledo, Ohio, and 40 miles (64 km) southwest of Detroit, the city is part of the Detroit–Ann Arbor–Flint combined statistical area.