Macomb County is a county located in the eastern portion of the U.S. state of Michigan. As of the 2010 census, the population was 840,978, making it the third-most populous county in the state. Of Michigan's five largest counties, Macomb experienced the most population growth (6.7%) between 2000 and 2010. The county seat is Mt. Clemens.Macomb County is part of the Detroit-Warren-Dearborn, MI Metropolitan Statistical Area.