Castro Valley is a census-designated place (CDP) in Alameda County, California, United States. At the 2010 census, it was the fifth most populous unincorporated area in California and the twenty-third most populous in the United States. The economy of Castro Valley consists largely of the provision of goods and services for local residents. Being a primarily residential community, only about 5% of the area has been developed for commercial uses.
Castro Valley is one of the sites where Joseph Eichler built some of the 10,000 or so homes he built in the Bay Area. Castro Valley has a one-screen movie theater, the Chabot Cinema. The Castro Village complex on Castro Valley Boulevard is widely considered the commercial center of town. The Harry Rowell Rodeo Ranch is located in Castro Valley and is managed by the Hayward Area Recreation and Park District. Rodeos are held there regularly.