Oak Park, CA. Online Offers. Oak Park is a census-designated place located in the Simi Hills, in Ventura County, California. As of the 2010 census, Oak Park had a population of 14,266, up from 14,225 at the 2000 census. It is located in the Conejo Valley, north from Malibu and Agoura Hills and is a part of Ventura County. Oak Park was formed from ranchland owned by Cosmo Stevens and Marian Jordan, stars of the radio show Fibber McGee and Molly. The land was purchased by Metropolitan Development Corporation in the 1940s and '50s.