Oakley is a city in Contra Costa County, California, United States. It is within the nine-county San Francisco Bay Area. The population was 35,432 at the 2010 U.S. Census. Oakley is part of the East Contra Costa Bicycle Plan, which has existing facilities in Oakley as well as plans for further expansion. Like many cities in California, the name "oak" comes from the abundance of oak trees, while the suffix "-ley" comes from the Old English word for "field" or "meadow."