Colorado has a total of 64 counties. The subject of which counties make up Metro Denver can be confusing.
The Denver Core Metropolitan Area, which dates back to 1902, consists of the City and County of Denver, Adams County, Arapahoe County, and Jefferson County. The Denver Central Metropolitan Area adds the City and County of Broomfield and Douglas County, for a total of six counties.
The Denver Region of the Denver Regional Council of Governments adds Boulder County, Clear Creek County, and Gilpin County to the Denver Central Metropolitan Area for a total of nine counties.
The Denver-Aurora-Lakewood, CO Metropolitan Statistical Area is made up of the counties of the Denver Region, minus Boulder County and plus Elbert County and Park County, for a total of ten counties. Boulder County then becomes the separate Boulder, CO Metropolitan Statistical Area.
The counties discussed here are the counties within the Denver Central Metropolitan Area. See this map of Metro Denver counties for their locations.
Adams County was created in 1902 and was named for Colorado Governor Alva Adams. Adams County has the fifth largest population of the 64 counties in Colorado.
The county seat is Brighton. Other cities within Adams County include Commerce City, Federal Heights, Northglenn, Thornton, and parts of Arvada, Aurora, and Westminster.
Size: Adams County has an area of 1,184 square miles.
Population: The estimated population in 2015 was 491,337.
Adjacent counties: Arapahoe, Denver, Jefferson, Broomfield, Weld, Morgan, and Washington
Arapahoe County was created in 1902. Today it's the third-most populous county in Colorado. The name comes from the Arapaho Native Americans who once lived there.
The county motto is “Colorado's First”. Littleton is the county seat of Arapahoe County. Other cities within the county include Centennial, Cherry Hills Village, Englewood, Greenwood Village, and part of Aurora.
Size: Arapahoe County has an area of 805 square miles.
Population: The estimated population in 2015 was 631,096.
Adjacent counties: Lincoln, Elbert, Douglas, Jefferson, Denver, Adams, and Washington
The city of Broomfield was incorporated in 1961 in what was then Boulder County. The name is believed to come from the fields of broom corn that used to grow there.
In 2001, Broomfield became a separate county. Broomfield is the newest and smallest county in Colorado, with the 13th largest population. Broomfield is also the newest county in the entire United States. Broomfield's motto is “A Great Place to Live, Work, and Play!”
Size: The City and County of Broomfield has an area of 34 square miles.
Population: The estimated population in 2015 was 65,065.
Adjacent counties: Adams, Jefferson, Boulder, and Weld
Denver is the capital of Colorado and has the largest population of any Colorado county. The City of Denver was founded in 1858. In 1902 it became the City and County of Denver. The area was originally part of Kansas Territory, and Denver was named for James W. Denver, the Governor of Kansas Territory. Denver's motto is “The Mile High City”.
Size: The City and County of Denver has an area of 155 square miles.
Population: The estimated population in 2015 was 682,545.
Adjacent counties: Arapahoe, Jefferson, and Adams
Douglas County was created in 1861 as one of the original 17 counties in what was then the Colorado Territory. The county was named for U.S. Senator Stephen A. Douglas of Illinois. Today Douglas County has the seventh largest population of the 64 counties in Colorado.
The county seat is Castle Rock. Other communities within Douglas County include Castle Pines, Castle Pines North, Highlands Ranch, Larkspur, Lone Tree, Parker, and parts of Aurora and Littleton.
Size: Douglas County has an area of 843 square miles.
Population: The estimated population in 2015 was 322,387.
Adjacent counties: Teller, El Paso, Jefferson, Arapahoe, and Elbert
Jefferson County was named for Thomas Jefferson, third U.S. President and author of the Declaration of Independence. Jefferson County is one of the original 17 counties of Colorado. It was created in 1861 as part of the Colorado Territory. Today Jefferson County is the fourth-most populous county in Colorado.
The county motto is "Gateway to the Rockies". The county seat is Golden. Other cities in Jefferson County include Edgewater, Lakewood, Wheat Ridge, and parts of Arvada, Littleton, and Westminster.
Size: Jefferson County has an area of 774 square miles.
Population: The estimated population in 2015 was 565,524.
Adjacent counties: Teller, Park, Clear Creek, Gilpin, Boulder, Broomfield, Adams, Denver, Arapahoe, and Douglas. Jefferson is one of the few counties in the United States to border this many other counties.
Photo: The Colorado State Capitol in Denver. The dome is covered in gold leaf to commemorate the Pike's Peak Gold Rush.