Monroe is a city in the U.S. state of Michigan. The population was 20,733 at the 2010 census. It is the largest city and county seat of Monroe County. The city is bordered on the south by Monroe Charter Township, but both are politically independent. The city is located approximately north of Toledo, Ohio and south of Detroit. The United States Census Bureau lists Monroe as the core city in the , which had a population of 152,021 in 2010. Monroe is officially part of the Detroit-Ann Arbor-Flint CSA. The city is sometimes unofficially included as a northerly extension of the Toledo Metropolitan Area.