# List of counties in Colorado

The 64 counties of the U.S. State of Colorado.
The U.S. State of Colorado is divided into 64 counties. Two of these, the City and County of Denver, which serves as the state capital, and the City and County of Broomfield, have consolidated city and county governments. Of the other 62 counties, all operate under Dillon's Rule except the two that are home rule (Pitkin and Weld). Counties are important units of government in Colorado since there are no civil townships or other minor civil divisions.
El Paso County, with a population of 730,395 in 2020, is the most populous county in Colorado, while San Juan County is the least populous, with a population of 705. Las Animas County, 4,776 square miles (12,369 km$^2$) in area, is the most extensive county, while the City and County of Broomfield, 34 square miles (87 km$^2$) in area, is the least extensive. The City and County of Denver is the most densely populated Colorado county, with a population density of 4,674 residents per square mile (1,805/km$^2$) as of 2020, while Hinsdale County is the least densely populated county, with a population density of 0.71 resident per square mile (0.27/km$^2$).
Mount Elbert, the highest summit of Colorado and the entire Rocky Mountains at an elevation of 14,440 feet (4,401.2 m), is located in Lake County. The lowest point in Colorado is where the Arikaree River flows out of Yuma County and into Kansas, at 3,317 feet (1,011 m) elevation. This point, which is the highest low point of any state, is higher than the highest points of 18 states and the District of Columbia.

## History

On November 1, 1861, the new Territory of Colorado created 17 original counties: Arapahoe, Boulder, Clear Creek, Costilla, Douglas, El Paso, Fremont, Gilpin, Guadalupe, Huerfano, Jefferson, Lake, Larimer, Park, Pueblo, Summit, and Weld; plus the Cheyenne Reserve. Six days later, the name of Guadelupe County was changed to Conejos County.
On February 9, 1866, the first new county, Las Animas, was created, followed by Saguache in December of that year. Bent County was created in February 1870, followed by Greenwood the following month. On February 2, 1874, Grand County and Elbert County were formed, and on February 10, La Plata, Hinsdale, and Rio Grande counties were created. Greenwood was absorbed into Bent on February 5. The last county to be created under the Colorado Territory name was San Juan County, created three months before statehood.
By the time Colorado became a state on August 1, 1876, it had only 26 counties. In January 1877, Routt and Ouray were formed, followed by Gunnison and Custer counties in March. In February 1879, Chaffee County was created. From February 8–10, 1879, Lake county was renamed Carbonate County. In 1881, Dolores County and Pitkin County were created. In 1883, Montrose, Mesa, Garfield, Eagle, Delta, and San Miguel counties were formed, leaving the total number of counties at 39. The number rose to 40 in 1885 with the creation of Archuleta County on April 14. Washington County and Logan County were both created in 1887. Between February 19 and April 16 in 1889, Morgan, Yuma, Cheyenne, Otero, Rio Blanco, Phillips, Sedgwick, Kiowa, Kit Carson, Lincoln, Prowers, Baca, and Montezuma counties were formed, bringing the total to 55. By 1900, Mineral County and Teller County had been added. On November 15, 1902, Arapahoe County was split into Adams and South Arapahoe Counties, and Denver was reconstituted as a consolidated city-county from portions of both newly formed counties on December 1, 1902. By 1912, Jackson County, Moffat County, and Crowley County had been created. Alamosa was created in 1913. In 2001, Broomfield was reconstituted as a consolidated city-county from parts of Adams, Boulder, Jefferson and Weld counties, bringing the total to 64 counties.

## List

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Select the OpenStreetMap link at the right to view the location of these 64 counties.
| County | FIPS code | County seat | Est. | Formed from | Etymology | Population | Area |
| Adams County | 001 | Brighton | Nov 15, 1902 | Split from Arapahoe County. | Named in honor of Alva Adams, the 5th, 10th, and 14th Governor of the State of Colorado. | 542,973 | 1,182.29 sq mi (3,062 km$^2$) |
| Alamosa County | 003 | Alamosa | Mar 8, 1913 | Split from Costilla County and Conejos County. | Named for the cottonwood trees which grow along the Rio Grande and its tributaries. Alamosa is a Spanish word for a cottonwood grove. | 16,689 | 723.21 sq mi (1,873 km$^2$) |
| Arapahoe County | 005 | Littleton | Nov 1, 1861 | Created as one of the 17 original counties of the Territory of Colorado. Renamed South Arapahoe County for the five months from November 15, 1902 to April 11, 1903. | Named for predecessor Arapahoe County, Kansas Territory, which in turn was named for the Arapaho Nation of Native Americans. | 666,918 | 804.41 sq mi (2,083 km$^2$) |
| Archuleta County | 007 | Pagosa Springs | Apr 14, 1885 | Split from Conejos County. | Named in honor of Colorado State Senator Antonio D. Archuleta and his father, José Manuel Archuleta. | 14,112 | 1,354.53 sq mi (3,508 km$^2$) |
| Baca County | 009 | Springfield | Apr 16, 1889 | Split from Las Animas County. | Named in honor of pioneer and Colorado territorial legislator Felipe Baca. | 3,367 | 2,558.48 sq mi (6,626 km$^2$) |
| Bent County | 011 | Las Animas | Feb 11, 1870 | Split from Huerfano County and former Cheyenne and Arapaho tribal land. | Named in honor of frontier trader William Bent. | 5,779 | 1,541.07 sq mi (3,991 km$^2$) |
| Boulder County | 013 | Boulder | Nov 1, 1861 | Created as one of the 17 original counties of the Territory of Colorado. | Named for the abundance of granite boulders along Boulder Creek. | 330,262 | 740.48 sq mi (1,918 km$^2$) |
| City and County of Broomfield | 014 | Broomfield | Nov 15, 2001 | Split from Boulder, Adams, Jefferson, and Weld counties and reorganized as a consolidated city and county. | Named for the broom corn that was formerly grown in the area. | 78,323 | 33.57 sq mi (87 km$^2$) |
| Chaffee County | 015 | Salida | Feb 10, 1879 | Split from Carbonate County. | Named in honor of Jerome Bunty Chaffee, one of Colorado's first two U.S. Senators from 1876 to 1879. | 20,780 | 1,014.12 sq mi (2,627 km$^2$) |
| Cheyenne County | 017 | Cheyenne Wells | Mar 25, 1889 | Split from Elbert and Bent counties. | Named for the Cheyenne Nation of Native Americans. | 1,712 | 1,781.90 sq mi (4,615 km$^2$) |
| Clear Creek County | 019 | Georgetown | Nov 1, 1861 | Created as one of the 17 original counties of the Territory of Colorado. | Named for Clear Creek which originates in the county. | 9,076 | 396.53 sq mi (1,027 km$^2$) |
| Conejos County | 021 | Conejos | Nov 1, 1861 | Guadalupe County, one of the 17 original counties of the Territory of Colorado, was renamed Conejos County after six days on November 7, 1861. | Named for the cottontail rabbits in the area. Conejos is a Spanish word for rabbits. | 7,549 | 1,290.22 sq mi (3,342 km$^2$) |
| Costilla County | 023 | San Luis | Nov 1, 1861 | Created as one of the 17 original counties of the Territory of Colorado. | Named for the Costilla River. Costilla is a Spanish word meaning either little rib or furring timber. | 3,686 | 1,229.38 sq mi (3,184 km$^2$) |
| Crowley County | 025 | Ordway | May 29, 1911 | Split from Otero County. | Named in honor of Colorado State Senator John H. Crowley. | 5,600 | 800.27 sq mi (2,073 km$^2$) |
| Custer County | 027 | Westcliffe | Mar 9, 1877 | Split from Fremont County. | Named in memory of George Armstrong Custer, (1839–1876), the U.S. Army colonel defeated and killed at the Battle of the Little Bighorn. | 5,553 | 739.24 sq mi (1,915 km$^2$) |
| Delta County | 029 | Delta | Feb 11, 1883 | Split from Gunnison County. | Named for the town of Delta located at the delta of the Uncompahgre River. | 32,215 | 1,149.44 sq mi (2,977 km$^2$) |
| City and County of Denver | 031 | Denver | Dec 1, 1902 | The original Arapahoe County Seat was split from Arapahoe and the newly-created Adams Counties, and reorganized as a consolidated city and county. | Named to curry favor with James W. Denver, Governor of the Territory of Kansas from 1857 to 1859. | 729,019 | 155.66 sq mi (403 km$^2$) |
| Dolores County | 033 | Dove Creek | Mar 4, 1881 | Split from Ouray County. | Named for the Dolores River, which was originally named el Rio de Nuestra Senora de los Dolores, which is Spanish for the River of our Lady of Sorrows. | 2,467 | 1,076.93 sq mi (2,789 km$^2$) |
| Douglas County | 035 | Castle Rock | Nov 1, 1861 | Created as one of the 17 original counties of the Territory of Colorado. | Named in honor of Stephen Arnold Douglas, (1813–1861), U.S. Senator from Illinois from 1847 to 1861. | 393,995 | 842.30 sq mi (2,182 km$^2$) |
| Eagle County | 037 | Eagle | Feb 11, 1883 | Split from Summit County. | Named for the Eagle River which originates in the county. | 54,330 | 1,700.76 sq mi (4,405 km$^2$) |
| El Paso County | 041 | Colorado Springs | Nov 1, 1861 | Created as one of the 17 original counties of the Territory of Colorado. | Named for Ute Pass, which connects the Great Plains to South Park and was formerly located within the county. El Paso means the pass in Spanish. | 752,772 | 2,128.60 sq mi (5,513 km$^2$) |
| Elbert County | 039 | Kiowa | Feb 2, 1874 | Split from Douglas County. | Named in honor of Samuel Hitt Elbert, the sixth Governor of the Territory of Colorado. | 29,382 | 1,849.08 sq mi (4,789 km$^2$) |
| Fremont County | 043 | Cañon City | Nov 1, 1861 | Created as one of the 17 original counties of the Territory of Colorado. | Named in honor of John Charles Frémont (1813–1890), the explorer, U.S. Army general, and U.S. Senator from California. | 50,093 | 1,533.09 sq mi (3,971 km$^2$) |
| Garfield County | 045 | Glenwood Springs | Feb 10, 1883 | Split from Summit County. | Named in honor of James Abram Garfield (1831–1881), the twentieth President of the United States. | 63,167 | 2,958.23 sq mi (7,662 km$^2$) |
| Gilpin County | 047 | Central City | Nov 1, 1861 | Created as one of the 17 original counties of the Territory of Colorado. | Named in honor of William Gilpin, the first Governor of the Territory of Colorado. | 5,963 | 150.15 sq mi (389 km$^2$) |
| Grand County | 049 | Hot Sulphur Springs | Feb 2, 1874 | Split from Summit County. | Named for the Grand River which originates in the county. The Grand River was renamed the Colorado River in 1921, but the county retains the original name. | 16,154 | 1,868.53 sq mi (4,839 km$^2$) |
| Gunnison County | 051 | Gunnison | Mar 9, 1877 | Split from Lake County. | Named in honor of John Williams Gunnison, the U.S. Army captain who explored the region. | 17,310 | 3,259.22 sq mi (8,441 km$^2$) |
| Hinsdale County | 053 | Lake City | Feb 10, 1874 | Split from Lake, Conejos, and Costilla counties. | Named in honor of George Aaron Hinsdale, a Lieutenant Governor of the Territory of Colorado. | 747 | 1,123.35 sq mi (2,909 km$^2$) |
| Huerfano County | 055 | Walsenburg | Nov 1, 1861 | Created as one of the 17 original counties of the Territory of Colorado. | Named for Huerfano Butte, a solitary volcanic plug. Huérfano is a Spanish word meaning orphan. | 6,988 | 1,592.37 sq mi (4,124 km$^2$) |
| Jackson County | 057 | Walden | May 5, 1909 | Split from Larimer County. | Named in honor of Andrew Jackson (1767–1845), the seventh President of the United States. | 1,273 | 1,619.75 sq mi (4,195 km$^2$) |
| Jefferson County | 059 | Golden | Nov 1, 1861 | Created as one of the 17 original counties of the Territory of Colorado. | Named for its extralegal predecessor county, Jefferson County, Jefferson Territory, which in turn was named in honor of Thomas Jefferson (1743–1826), the author of the Declaration of Independence and the third President of the United States. | 578,533 | 772.85 sq mi (2,002 km$^2$) |
| Kiowa County | 061 | Eads | Apr 11, 1889 | Split from Bent County. | Named for the Kiowa Nation of Native Americans. | 1,392 | 1,785.90 sq mi (4,625 km$^2$) |
| Kit Carson County | 063 | Burlington | Apr 11, 1889 | Split from Elbert County. | Named in honor of Christopher Houston "Kit" Carson, the famous frontier scout and soldier. | 7,080 | 2,162.43 sq mi (5,601 km$^2$) |
| La Plata County | 067 | Durango | Feb 10, 1874 | Split from Lake and Conejos counties. | Named for the many silver deposits in the area. La plata is a Spanish expression for the silver. | 56,823 | 1,700.44 sq mi (4,404 km$^2$) |
| Lake County | 065 | Leadville | Nov 1, 1861 | Created as one of the 17 original counties of the Territory of Colorado. Renamed Carbonate County for the two days from February 8–10, 1879. | Named for the Twin Lakes in the county. | 7,369 | 383.55 sq mi (993 km$^2$) |
| Larimer County | 069 | Fort Collins | Nov 1, 1861 | Created as one of the 17 original counties of the Territory of Colorado. | Named in honor of William Larimer, a pioneer entrepreneur. | 374,574 | 2,631.75 sq mi (6,816 km$^2$) |
| Las Animas County | 071 | Trinidad | Feb 9, 1866 | Split from Huerfano County. | Named for the Purgatoire River, which was originally named el Rio de las Animas Perdidas, which is Spanish for the River of the Souls in Purgatory. | 14,518 | 4,773.27 sq mi (12,363 km$^2$) |
| Lincoln County | 073 | Hugo | Apr 11, 1889 | Split from Elbert and Bent counties. | Named in honor of Abraham Lincoln (1809–1865), the sixteenth President of the United States. | 5,598 | 2,585.21 sq mi (6,696 km$^2$) |
| Logan County | 075 | Sterling | Feb 25, 1887 | Split from Weld County. | Named in honor of John Alexander Logan (1826–1886), a U.S. Army general and U.S. Senator from Illinois. | 20,755 | 1,845.31 sq mi (4,779 km$^2$) |
| Mesa County | 077 | Grand Junction | Feb 14, 1883 | Split from Gunnison County. | Named for the mesa formations which are widespread through the area. | 161,260 | 3,345.69 sq mi (8,665 km$^2$) |
| Mineral County | 079 | Creede | Mar 27, 1893 | Split from Hinsdale, Rio Grande, and Saguache counties. | Named from the plentiful mineral deposits found in the area. | 933 | 878.16 sq mi (2,274 km$^2$) |
| Moffat County | 081 | Craig | Feb 27, 1911 | Split from Routt County. | Named in honor of railroad pioneer David H. Moffat. | 13,142 | 4,755.86 sq mi (12,318 km$^2$) |
| Montezuma County | 083 | Cortez | Apr 16, 1889 | Split from La Plata County. | Named in honor of Aztec leader Moctezuma II. Ruins in the area were once thought to be Aztec. | 26,841 | 2,035.80 sq mi (5,273 km$^2$) |
| Montrose County | 085 | Montrose | Feb 11, 1883 | Split from Gunnison County. | Named for the town of Montrose, which in turn was probably named from the novel A Legend of Montrose, published in 1819 by Walter Scott. | 44,806 | 2,246.43 sq mi (5,818 km$^2$) |
| Morgan County | 087 | Fort Morgan | Feb 19, 1889 | Split from Weld County. | Named for old Fort Morgan, which in turn was named in honor of U.S. Army Colonel Christopher A. Morgan. | 30,300 | 1,293.83 sq mi (3,351 km$^2$) |
| Otero County | 089 | La Junta | Mar 25, 1889 | Split from Bent County. | Named in honor of Miguel A. Otero of the prominent Otero family of the Southwest. | 17,991 | 1,267.66 sq mi (3,283 km$^2$) |
| Ouray County | 091 | Ouray | Jan 18, 1877 | Split from Hinsdale and Lake counties. Renamed Uncompaghre County for four days from 1883-02-27, to 1883-03-02. | Named in honor of Ouray, a Ute Native American leader. | 5,197 | 542.30 sq mi (1,405 km$^2$) |
| Park County | 093 | Fairplay | Nov 1, 1861 | Created as one of the 17 original counties of the Territory of Colorado. | Named for South Park which occupies most of the county. | 18,316 | 2,209.36 sq mi (5,722 km$^2$) |
| Phillips County | 095 | Holyoke | Mar 27, 1889 | Split from Logan County. | Named in honor of R.O. Phillips, secretary of the Lincoln Land Company, which sold farmsteads in the area. | 4,488 | 688.30 sq mi (1,783 km$^2$) |
| Pitkin County | 097 | Aspen | Feb 23, 1881 | Split from Gunnison County. | Named in honor of Frederick Walker Pitkin, the second Governor of the State of Colorado. | 16,643 | 970.37 sq mi (2,513 km$^2$) |
| Prowers County | 099 | Lamar | Apr 11, 1889 | Split from Bent County. | Named in honor of John W. Prowers, a pioneer of the Arkansas River valley. | 11,957 | 1,645.37 sq mi (4,261 km$^2$) |
| Pueblo County | 101 | Pueblo | Nov 1, 1861 | Created as one of the 17 original counties of the Territory of Colorado. | Named for historic town of Pueblo. Pueblo is a Spanish word meaning village or people. | 169,866 | 2,396.77 sq mi (6,208 km$^2$) |
| Rio Blanco County | 103 | Meeker | Mar 25, 1889 | Split from Garfield County. | Named for the White River, which was originally named Rio Blanco in Spanish. | 6,607 | 3,226.24 sq mi (8,356 km$^2$) |
| Rio Grande County | 105 | Del Norte | Feb 10, 1874 | Split from Costilla County and Conejos County counties. | Named for the Rio Grande, which flows through the area. | 11,132 | 913.10 sq mi (2,365 km$^2$) |
| Routt County | 107 | Steamboat Springs | Jan 29, 1877 | Split from Grand County. | Named in honor of John Long Routt, the first Governor of the State of Colorado. | 25,243 | 2,362.11 sq mi (6,118 km$^2$) |
| Saguache County | 109 | Saguache | Dec 29, 1866 | Split from Lake and Costilla counties. | Name comes from a Ute language noun meaning "sand dunes". | 6,670 | 3,168.32 sq mi (8,206 km$^2$) |
| San Juan County | 111 | Silverton | Jan 31, 1876 | Split from Lake County. | Named for the San Juan River and San Juan Mountains, which in turn were named for Saint John the Evangelist. | 821 | 388.99 sq mi (1,007 km$^2$) |
| San Miguel County | 113 | Telluride | Mar 2, 1883 | Split from San Juan County. | Named for the San Miguel River and San Miguel Mountains, which in turn were named for Saint Michael the Archangel. | 7,819 | 1,290.76 sq mi (3,343 km$^2$) |
| Sedgwick County | 115 | Julesburg | Apr 9, 1889 | Split from Logan County. | Named for Fort Sedgwick, which, in turn, was named for U.S. Army General John Sedgwick (1813–1864). | 2,257 | 548.83 sq mi (1,421 km$^2$) |
| Summit County | 117 | Breckenridge | Nov 1, 1861 | Created as one of the 17 original counties of the Territory of Colorado. | Named for the many high mountain summits in the area. | 30,882 | 618.92 sq mi (1,603 km$^2$) |
| Teller County | 119 | Cripple Creek | Mar 23, 1899 | Split from El Paso and Fremont counties. | Named in honor of Henry Moore Teller, a U.S. Senator from Colorado and United States Secretary of the Interior. | 24,862 | 558.58 sq mi (1,447 km$^2$) |
| Washington County | 121 | Akron | Feb 9, 1887 | Split from Weld County. | Named in honor of George Washington (1732–1799), the first President of the United States. | 4,771 | 2,522.90 sq mi (6,534 km$^2$) |
| Weld County | 123 | Greeley | Nov 1, 1861 | Created as one of the 17 original counties of the Territory of Colorado. | Named in honor of Lewis Ledyard Weld, the first Secretary of the Territory of Colorado. | 369,745 | 4,013.84 sq mi (10,396 km$^2$) |
| Yuma County | 125 | Wray | Mar 15, 1889 | Split from Washington County. | Named for the Quechan (Yuma) Nation of Native Americans. | 10,048 | 2,369.61 sq mi (6,137 km$^2$) |

## 2024 population estimates

For United States Census Bureau population estimates for Colorado counties as of July 1, 2024, see the List of Colorado counties by population. That list ranks the counties by 2024 population and includes population changes since the 2000 United States Census. That list also includes the county websites, links to Colorado Department of Transportation county maps, and the geographic coordinates of the counties.
As of July 1, 2024, El Paso County remains the most populous county in Colorado with a population estimate of 752,772, while Hinsdale County with a 2024 population of 747 is now the least populous. Five of the 64 Colorado counties now have more than 500,000 residents, while 12 counties have fewer than 5,000 residents.

## Former counties

The following sortable table lists all the historic counties of the Territory of New Mexico, the Territory of Utah, the Territory of Kansas, and the extralegal Territory of Jefferson that previously existed within the boundaries of the present State of Colorado, as well as the three defunct counties of the Territory of Colorado and the three defunct counties of the State of Colorado.
Counties formerly within the area of the State of Colorado :
| County | Territory or State | Date created | Date superseded | History |
| Taos County | Territory of New Mexico | 1852-01-09 | 1861-02-28 | Originally one of the seven partidos of the Spanish, and later Mexican, province of Santa Fe de Nuevo México. One of the nine original counties created by the Territory of New Mexico in 1852. Excluded from the new Territory of Colorado in 1861. |
| Great Salt Lake County | Territory of Utah | 1852-03-03 | 1861-02-28 | Created in 1852. Excluded from the new Territory of Colorado in 1861. |
| Green River County | Territory of Utah | 1852-03-03 | 1861-02-28 | Created in 1852, but never organized. Dissolved in 1857, but recreated in 1859. Excluded from the new Territory of Colorado in 1861, and the Territory of Wyoming in 1868. Finally dissolved in 1872. |
| Iron County | Territory of Utah | 1852-03-03 | 1861-02-28 | Created in 1852. Excluded from the new Territory of Colorado in 1861. |
| Sanpete County | Territory of Utah | 1852-03-03 | 1861-02-28 | Created in 1852. Excluded from the new Territory of Colorado in 1861. |
| Utah County | Territory of Utah | 1852-03-03 | 1861-02-28 | Created in 1852. Excluded from the new Territory of Colorado in 1861. |
| Washington County | Territory of Utah | 1852-03-03 | 1861-02-28 | Created in 1852. Excluded from the new Territory of Colorado in 1861. |
| Arapahoe County | Territory of Kansas | 1855-08-25 | 1861-01-29 | Created in 1855, but never organized. Reverted to unorganized territory when Kansas joined the Union in 1861. |
| Beaver County | Territory of Utah | 1856-01-05 | 1861-02-28 | Split from Iron and Millard counties in 1856. Excluded from the new Territory of Colorado in 1861. |
| Broderick County | Territory of Kansas | 1859-02-07 | 1861-01-29 | Split from Arapahoe County in 1859, but never organized. Reverted to unorganized territory when Kansas joined the Union in 1861. |
| El Paso County | Territory of Kansas | 1859-02-07 | 1861-01-29 | Split from Arapahoe County in 1859, but never organized. Reverted to unorganized territory when Kansas joined the Union in 1861. |
| Fremont County | Territory of Kansas | 1859-02-07 | 1861-01-29 | Split from Arapahoe County in 1859, but never organized. Reverted to unorganized territory when Kansas joined the Union in 1861. |
| Montana County | Territory of Kansas | 1859-02-07 | 1861-01-29 | Split from Arapahoe County in 1859, but never organized. Reverted to unorganized territory when Kansas joined the Union in 1861. |
| Oro County | Territory of Kansas | 1859-02-07 | 1861-01-29 | Split from Arapahoe County in 1859, but never organized. Reverted to unorganized territory when Kansas joined the Union in 1861. |
| Peketon County | Territory of Kansas | 1859-02-07 | 1861-01-29 | Created in 1859, but never organized. Reverted to unorganized territory when Kansas joined the Union in 1861. |
| Arapahoe County | Territory of Jefferson | 1859-11-28 | 1861-02-28 | One of the 12 counties created by the extralegal Territory of Jefferson in 1859. |
| Cheyenne County | Territory of Jefferson | 1859-11-28 | 1861-02-28 | One of the 12 counties created by the extralegal Territory of Jefferson in 1859. |
| El Paso County | Territory of Jefferson | 1859-11-28 | 1861-02-28 | One of the 12 counties created by the extralegal Territory of Jefferson in 1859. |
| Fountain County | Territory of Jefferson | 1859-11-28 | 1861-02-28 | One of the 12 counties created by the extralegal Territory of Jefferson in 1859. |
| Heele County | Territory of Jefferson | 1859-11-28 | 1861-02-28 | One of the 12 counties created by the extralegal Territory of Jefferson in 1859. |
| Jackson County | Territory of Jefferson | 1859-11-28 | 1861-02-28 | One of the 12 counties created by the extralegal Territory of Jefferson in 1859. |
| Jefferson County | Territory of Jefferson | 1859-11-28 | 1861-02-28 | One of the 12 counties created by the extralegal Territory of Jefferson in 1859. |
| Mountain County | Territory of Jefferson | 1859-11-28 | 1861-02-28 | One of the 12 counties created by the extralegal Territory of Jefferson in 1859. |
| North County | Territory of Jefferson | 1859-11-28 | 1861-02-28 | One of the 12 counties created by the extralegal Territory of Jefferson in 1859. |
| Park County | Territory of Jefferson | 1859-11-28 | 1861-02-28 | One of the 12 counties created by the extralegal Territory of Jefferson in 1859. |
| St. Vrain County | Territory of Jefferson | 1859-11-28 | 1861-02-28 | One of the 12 counties created by the extralegal Territory of Jefferson in 1859. |
| Saratoga County | Territory of Jefferson | 1859-11-28 | 1861-02-28 | One of the 12 counties created by the extralegal Territory of Jefferson in 1859. |
| Mora County | Territory of New Mexico | 1860-02-01 | 1861-02-28 | Split from Taos County and San Miguel County in 1860. Excluded from the new Territory of Colorado in 1861. |
| Guadalupe County | Territory of Colorado | 1861-11-01 | 1861-11-07 | One of the 17 original counties created by the Territory of Colorado in 1861. The county was renamed Conejos County after only six days. |
| Greenwood County | Territory of Colorado | 1870-02-11 | 1874-02-06 | Created from expropriated Cheyenne and Arapaho tribal land and the eastern portion of Huerfano County in 1870. The county was abolished in 1874 and its territory split between Elbert County and Bent County. |
| Platte County | Territory of Colorado | 1872-02-09 | 1874-02-09 | Created from the eastern portion of Weld County in 1872. The county was abolished in 1874 after organizers failed to secure voter approval. The territory of the county was returned to Weld County. |
| Carbonate County | State of Colorado | 1879-02-08 | 1879-02-10 | Lake County was renamed Carbonate County in 1879. Only two days later, Carbonate County was split into the new Chaffee County and a recreated Lake County. |
| Uncompahgre County | State of Colorado | 1883-02-27 | 1883-03-02 | Ouray County was renamed Uncompahgre County for only four days in 1883. |
| South Arapahoe County | State of Colorado | 1902-11-15 | 1903-04-11 | One of three counties created from Arapahoe County in 1902. The name was changed back to Arapahoe County after five months. |

## County high points

Of the 64 Colorado counties, 20 counties extend above 14,000 feet (4,267 m) elevation, 32 counties extend above 13,000 feet (3,962 m), 42 counties extend above 10,000 feet (3,048 m), and all 64 Colorado counties extend above 4,116 feet (1,255 m).

## County mean elevation

Of Colorado's 64 counties, 4 counties have a mean elevation above 11,000 feet (3,353 m) elevation, 22 counties have a mean elevation above 10,000 feet (3,048 m), 32 counties have a mean elevation above 9,000 feet (2,743 m), and all 64 counties have a mean elevation above 3,880 feet (1,183 m).
The following 13 Colorado counties have highest mean elevation of any county in the United States, exceeding even the Denali Borough of Alaska.
The 13 highest mean elevation counties in the United States :
| Rank | County | Mean elevation | High point | Highest elevation | Low point | Lowest elevation | Elevation range |
| 1 | Lake County | 11,702.5 feet 3,567 m | Mount Elbert | 14,440 feet 4,401 m | Arkansas River | 8,965 feet 2,733 m | 5,475 feet 1,669 m |
| 2 | Hinsdale County | 11,300 feet 3,444 m | Uncompahgre Peak | 14,315 feet 4,363 m | Lake Fork Gunnison River | 8,285 feet 2,525 m | 6,030 feet 1,838 m |
| 3 | Mineral County | 11,116 feet 3,388 m | Phoenix Peak | 13,902 feet 4,237 m | Rio Grande | 8,330 feet 2,539 m | 5,572 feet 1,698 m |
| 4 | San Juan County | 11,085 feet 3,379 m | Vermilion Peak | 13,900 feet 4,237 m | Animas River | 8,270 feet 2,521 m | 5,630 feet 1,716 m |
| 5 | Summit County | 10,935.5 feet 3,333 m | Grays Peak | 14,276 feet 4,351 m | Blue River | 7,595 feet 2,315 m | 6,681 feet 2,036 m |
| 6 | Alamosa County | 10,928.5 feet 3,331 m | Blanca Peak | 14,351 feet 4,374 m | Rio Grande | 7,506 feet 2,288 m | 6,845 feet 2,086 m |
| 7 | Saguache County | 10,915 feet 3,327 m | Crestone Peak | 14,300 feet 4,359 m | San Luis Creek | 7,530 feet 2,295 m | 6,770 feet 2,063 m |
| 8 | Costilla County | 10,865.5 feet 3,312 m | Blanca Peak | 14,351 feet 4,374 m | Rio Grande | 7,380 feet 2,249 m | 6,971 feet 2,125 m |
| 9 | Park County | 10,705.5 feet 3,263 m | Mount Lincoln | 14,293 feet 4,357 m | South Platte River | 7,118 feet 2,170 m | 7,175 feet 2,187 m |
| 10 | Chaffee County | 10,661 feet 3,249 m | Mount Harvard | 14,427 feet 4,397 m | Arkansas River | 6,895 feet 2,102 m | 7,532 feet 2,296 m |
| 11 | Clear Creek County | 10,608 feet 3,233 m | Grays Peak | 14,276 feet 4,351 m | Clear Creek | 6,940 feet 2,115 m | 7,336 feet 2,236 m |
| 12 | Rio Grande County | 10,402 feet 3,171 m | Bennett Peak | 13,209 feet 4,026 m | Rock Creek | 7,595 feet 2,315 m | 5,614 feet 1,711 m |
| 13 | Jackson County | 10,353 feet 3,156 m | Clark Peak | 12,956 feet 3,949 m | North Platte River | 7,750 feet 2,362 m | 5,206 feet 1,587 m |

## County firsts

    1. Costilla County was the first area within the present State of Colorado to be settled by Europeans in 1851.
    2. Taos County, created by the Territory of New Mexico in 1852, was the first organized county to extend into the area of the present State of Colorado.
    3. Arapahoe County, created by the Territory of Kansas in 1855, was the first county created exclusively within the area of the present State of Colorado.
    4. On November 28, 1859, the extralegal Territory of Jefferson created 12 counties:
The 12 counties of the Territory of Jefferson :
| County | County Seat |
| Arapahoe County | Denver City |
| Cheyenne County | |
| El Paso County | Colorado City |
| Fountain County | Pueblo |
| Heele County | La Porte |
| Jackson County | Boulder City |
| Jefferson County | Arapahoe City Golden City |
| Mountain County | Central City |
| North County | |
| Park County | Tarryall City |
| Saint Vrain's CountySt. Vrain's County | Saint VrainSt. Vrain |
| Saratoga County | Breckinridge |
    5. On November 1, 1861, the Territory of Colorado created the 17 original Colorado counties:
The 17 original counties of the Territory of Colorado :
| County | First County Seat |
| Arapahoe County | Denver City |
| Boulder County | Boulder City |
| Clear Creek County | Idaho |
| Costilla County | San Miguel |
| Douglas County | Frankstown |
| El Paso County | Colorado City |
| Fremont County | Cañon City |
| Gilpin County | Central City |
| Guadaloupe County | Guadaloupe |
| Huerfano County | Autobees Plaza |
| Jefferson County | Golden City |
| Lake County | Oro City |
| Larimer County | La Porte |
| Park County | Tarryall City |
| Pueblo County | Pueblo |
| Summit County | Parkville |
| Weld County | Saint VrainSt. Vrain |
    6. Of the 17 original Colorado counties created in 1861, only Gilpin County and Clear Creek County have retained their original boundaries with only minor survey changes.
    7. Guadaloupe County was the first Colorado county to be renamed after only six days in 1861.
    8. Las Animas County was the first new Colorado county to be created (in 1866) after the original 17 counties.
    9. Greenwood County was the longest lived former Colorado county, existing four years from 1870 to 1874.
    10. In 1876, San Juan County became the last county created by the Territory of Colorado, bringing the total number of territorial counties to 26.
    11. In 1877, Ouray County became the first county created by the new State of Colorado.
    12. Carbonate County was the shortest lived former Colorado county, existing only two days in 1879 before being dissolved.
    13. The City and County of Broomfield became the newest Colorado county in 2001, bring the total number of counties to 64.

## County distinctions

    1. El Paso County (88) and the City and County of Denver (93) and are among the 100 most populous counties of the United States.
    2. San Juan County (16), Hinsdale County (25), Mineral County (32), Jackson County (55), Kiowa County (59), and Cheyenne County (80) are among the 100 least populous counties of the United States.
    3. Jefferson County borders ten adjacent counties, the most of any Colorado county.
    4. Delta County and the City and County of Denver each border only three adjacent counties, the fewest of Colorado counties.
    5. Weld County has the most incorporated municipalities of any Colorado county with 31.
    6. The following nine Colorado counties have no incorporated municipalities other than their county seat:
| County | County Seat |
| Archuleta County | Town of Pagosa Springs |
| Bent County | City of Las Animas |
| City and County of Broomfield ||
| City and County of Denver ||
| Hinsdale County | Town of Lake City |
| Jackson County | Town of Walden |
| Lake County | City of Leadville |
| Mineral County | Town of Creede |
| San Juan County | Town of Silverton |
    7. Of all 64 Colorado counties, only Conejos County has a county seat that is not an incorporated municipality.
    8. The City and County of Denver and the City and County of Broomfield are the only two Colorado counties with enclaves. Arapahoe County, Boulder County, and Jefferson County are the only three Colorado counties with exclaves.
    9. Pitkin and Weld are the only home rule counties.

## Gallery

* The ten most populous Colorado counties
* 1. The United States Air Force Academy in El Paso County, Colorado
* 2. The Colorado State Capitol in the City and County of Denver
* 3. A bank building in Arapahoe County, Colorado
* 4. The Colorado School of Mines in Jefferson County, Colorado
* 5. The Anschutz Medical Campus in Adams County, Colorado
* 6. Roxborough State Park in Douglas County, Colorado
* 7. Colorado State University in Larimer County, Colorado
* 8. The Greeley Stampede Parade in Weld County, Colorado
* 9. The National Center for Atmospheric Research in Boulder County, Colorado
* 10. The Historic Arkansas Riverwalk in Pueblo County, Colorado