Macomb County is a county located in the eastern portion of the U.S. state of Michigan, bordering Lake St. Clair, and is part of northern Metro Detroit. As of the 2020 Census, the population was 881,217, making it the third-most populous county in the state. The county seat is Mt. Clemens. Macomb County is part of the Detroit-Warren-Dearborn, MI Metropolitan Statistical Area. The city of Detroit is located on the county's southern border.