Clayton is a city in Contra Costa County, California, United States. The population was 10,897 as of the 2010 census.
According to the United States Census Bureau, the city has a total area of 3.8 square miles, all land. Clayton is located at the foot of Mt. Diablo State Park.
The public schools of which the minors of Clayton attend include: Mt.Diablo Elementary School, Highlands Elementary School, Diablo View Middle School, Pine Hollow Middle School, and Clayton Valley High School.
The Clayton branch of the Contra Costa County Library system is located in Clayton.