Douglas County Real Estate View 944 listings HomeGuidesDouglas County Douglas County is the seventh-most populous of the 64 counties of the U.S. state of Colorado. As of the 2010 census, the population was 285,465. The county seat is Castle Rock. Wikipedia Area: 840 mi² Population: 322,387 (2015) County seat: Castle Rock Points of interest: Colorado Trail, Pike National Forest, MORE Did you know: Douglas is the fourth-highest-income Colorado location by per capita income ($42,418). wikipedia.org Guides MonumentColorado SpringsCastle RockLarkspurWoodmoorKing’s DeerBent TreeGleneagleEl Paso CountyDouglas CountyPalmer LakeBlack Forest