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 96,000, is an unincorporated CDP). In recent years, Parker has become a commuter town at the southeasternmost corner of the Denver metropolitan area. As of the 2010 census the town population was 45,297; the estimated population in 2019 was 57,706. Parker is now the 19th most populous municipality in the state of Colorado.