About This Place
Castro Valley is a census-designated place (CDP) 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.
Before the arrival of European settlers the area was settled by the Chocheño (also spelled Chochenyo or Chocenyo) subdivision of the Ohlone Native Americans.
With the arrival of Europeans, Castro Valley was part of the land granted to Mission San Jose in 1797. The area Castro Valley now occupies was part of the extensive colony of New Spain in what was the state of Alta California.