Castro Valley is an unincorporated community in Alameda County, California, located in the picturesque East Bay hills of the Greater San Francisco Bay Area. It sits alongside Interstate 580 south of Oakland, east of San Leandro and north of Hayward, and borders Lake Chabot and the East Bay Regional Park District.
Named after Mexican Army soldier and rancher Don Guillermo Castro, it was part of an original 28,000 acre land grant known as Rancho San Lorenzo, which included Castro Valley, San Lorenzo, Hayward, Crow Canyon, Cull Canyon and Palomares Canyon.
During the early part of the 20th Century is was largely an agricultural area famous for its many chicken ranches (and its bootleg "stills" during Prohibition).
Today, as a thriving suburban community noted for its excellent schools, it retains much of its former rural character. The community's major event each year is the popular Rowell Ranch Rodeo with its parade and many accompanying activities.Its average elevation is 180 feet above sea level.
Its land area is approximately 14.4 square miles with a population density of 3,972 people per square mile. As of the 2000 Census, it is the fifth most populous unincorporated area in California, and the twenty-third in the United States. Being unincorporated, it is governed by Alameda County and has no city services. To date, all efforts to incorporate Castro Valley have been voted down by its residents.