Parker is a home rule municipality in Douglas County, Colorado, United States. As a self-declared "town" under the home rule statutes, Parker is the second most populous town in the county; Castle Rock is the most populous (the community of Highlands Ranch, with a population of over 100,000, is an unincorporated CDP). In recent years, Parker has become a commuter town at the southeasternmost corner of the Denver metropolitan area. The population was 58,512 at the 2020 census. Parker is now the 19th most populous municipality in the state of Colorado.