Oakdale is a city in Stanislaus County, California, United States. The population was 15,503 at the 2000 census. 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". As of January 2009 the population had reached 20,084 residents.