Brentwood is a city in Contra Costa County, California, United States. It is located in the East Bay region of the San Francisco Bay Area. The population is 51,481 as of 2010, an increase of 121 percent from 23,302 at the 2000 census. Brentwood began as a community in the late 19th century, and still is known throughout the Bay Area for its agricultural products, primarily its cherries, corn and peaches.