Smithville is a city in Clay and Platte counties in the U.S. state of Missouri and is part of the Kansas City metropolitan area, along the Little Platte River. The population was 10,406 at the 2020 United States Census.

Clay County is located in the U.S. state of Missouri and is part of the Kansas City metropolitan area. As of the 2020 census, the county had a population of 253,335, 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 a member of the United States Senate and United States Secretary of State.