Clayton (formerly Clayton's and Claytonville) is a city in Contra Costa County, California, United States. The population was 10,897 as of the 2010 census.
In 1857, the town of Clayton was laid out and founded by Joel Henry Clayton (1812–1872) and his two younger brothers. Clayton was born in Bugsworth, now Buxworth, in the United Kingdom, and emigrated to the United States in 1837. After years in other states he settled down with his wife Margaret (1820–1908) at his town at the foot of Mount Diablo, where he and his family prospered. Clayton was named after Joel Henry Clayton, although only by the flip of a coin. Joel Clayton and Charles Rhine cofounded the town, and each wanted to name it after himself. If Charles had won it would have become Rhinesville, but Joel Clayton won. Joel and his wife Margaret both died in Clayton, and were buried in Live Oak Cemetery in what is now Concord, CA.
Clayton prospered during the coal mining boom in eastern Contra Costa County. The post office opened in 1861.