Castro Valley Map
Castro Valley Information
Castro Valley
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 population was 66,441 at the 2020 census.Castro Valley is named after Don Guillermo Castro, a noted 19th-century Californio ranchero who owned the land where the community is located.