Oakdale is a city in Stanislaus County, California, United States. It is part of the Modesto Metropolitan Statistical Area. The city was founded in 1871 when the Stockton & Visalia Railroad met the Copperopolis Railroad. Oakdale goes by the slogan "Cowboy Capital of the World. " The population was 20,675 at the 2010 census, up from 15,503 at the 2000 census.