Clinton is a city in Henry County, Missouri, United States. The population was 9,174 at the 2020 census. It is the county seat of Henry County. Clinton was laid out in 1836. The city was named for New York Governor DeWitt Clinton, a key promoter of the Erie Canal. A post office called Clinton has been in operation since 1850. The railroad reached Clinton in 1870, when the Census put the population at 840.