Castro Valley is a census-designated place in Alameda County, California, United States. As of the 2000 census, it is the fifth most populous unincorporated area in California, and the twenty-third in the United States. The population was 61,388 at the 2010 census.
Lake Chabot lies at the north of Castro Valley. The eastern hills of Castro Valley constitute the headwaters of the San Lorenzo Creek watershed and the origin of several creeks that flow into San Lorenzo Creek.
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.
Castro Valley is served by the Castro Valley Unified School District. The school district includes the Castro Valley Adult School.
Castro Valley also holds a private elementary school and preschool called Camelot Elementary.