Clinton County is a county located in the U.S. state of Missouri and is part of the Kansas City metropolitan area. As of the 2020 U.S. Census, the county had a population of 21,184. 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 its 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.