There are 19 US Post Offices in Macomb County serving a total of 386,432 residents equating to 20,339 residents per post office. It's estimated that approximately 616,789 packages are handled across the 19 county post offices annually. 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. The city of Detroit is located south of 8 Mile Road, the county's southern border. Macomb County contains 27 cities, townships and villages, including three of the top ten most populous municipalities in Michigan as of the 2010 census: Warren (#3), Sterling Heights (#4) and Clinton Township (#10). Most of this population is concentrated south of Hall Road (M-59), one of the county's main thoroughfares."