Clayton is a city located in the state of Missouri within the United States. It serves as the county seat of St. Louis County and shares a border with the west side of the independent city of St. Louis.
The city was organized in 1877 and was named in honor of Ralph Clayton, a local citizen who donated the land used for the construction of the St. Louis County courthouse. As of the 2020 census, the population of Clayton was 17,355.