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 51,300 as of 2010 . Over the past several years a great deal of big-box retail has been introduced in the area of the Brentwood/Antioch border on Lone Tree Way at the SR 4 Bypass, about 3.5 miles from downtown Brentwood. This includes major tenants such as Kohl's, Khoa's, Trader Joe's, Home Depot, Lowes. Slatten Ranch shopping center, actually on the Antioch side of Lone Tree Way, includes Target, Sport Chalet and Barnes & Noble. J. C. Penney opened its Slatten Ranch store in March 2008.