There are 6 US Post Offices in Clinton County serving a total of 25,722 residents equating to 4,287 residents per post office. It's estimated that approximately 41,055 packages are handled across the 6 county post offices annually. Clinton County is a county located in the U.S. state of Missouri. As of the 2010 census, the county had a population of 20,743. Its county seat is Plattsburg. The county was organized January 2, 1833 and named for Governor DeWitt Clinton of New York. The county seat of Plattsburg derives it name from a town of a similar name that is the county seat of Clinton County, New York, which was also named for the Governor. Clinton County is part of the Kansas City, MO-KS Metropolitan Statistical Area."