There are 11 US Post Offices in Clay County serving a total of 209,846 residents equating to 19,077 residents per post office. It's estimated that approximately 334,938 packages are handled across the 11 county post offices annually. Clay County is a county located in the U.S. state of Missouri. As of the 2010 census, the county had a population of 221,939, making it the fifth-most populous county in Missouri. Its county seat is Liberty. The county was organized January 2, 1822, and named in honor of U.S. Representative Henry Clay from Kentucky, later member of the United States Senate and United States Secretary of State. Clay County is part of the Kansas City, MO-KS Metropolitan Statistical Area and contains many of the city's northern suburbs, along with a substantial portion of the City of Kansas City. Clay County owns and operates the Midwest National Air Center in Excelsior Springs."