Castle Rock is a home rule town that is the county seat of and the most-populous municipality in Douglas County, Colorado, United States. The town's population was 73,158 at the 2020 census, a 51.68% increase since the 2010 census. Castle Rock is the most-populous Colorado town and the 14th-most populous Colorado municipality. Castle Rock is a part of the Denver-Aurora-Lakewood, CO metropolitan statistical area and the Front Range urban corridor.