County
| FIPS code[4] [a] | County seat[5] [6] | Est. [7] | Formed from[7] | Etymology[7] | Population[8] | Area[5] | Map |
| Adams County | 001 | Brighton | 1902-11-15 | Split from Arapahoe County. | Named in honor of Alva Adams, the 5th, 10th, and 14th Governor of the State of Colorado. | 519,572 | 1,182.29 sq mi
(3,062 km2) |  |
| Alamosa County | 003 | Alamosa | 1913-03-08 | 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. | 16,376 | 723.21 sq mi
(1,873 km2) |  |
| Arapahoe County | 005 | Littleton | 1861-11-01 | 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. | 655,070 | 804.41 sq mi
(2,083 km2) |  |
| Archuleta County | 007 | Pagosa Springs | 1885-04-14 | Split from Conejos County. | Named in honor of Colorado State Senator Antonio D. Archuleta and his father, José Manuel Archuleta. | 13,359 | 1,354.53 sq mi
(3,508 km2) |  |
| Baca County | 009 | Springfield | 1889-04-16 | Split from Las Animas County. | Named in honor of pioneer and Colorado territorial legislator Felipe Baca. | 3,506 | 2,558.48 sq mi
(6,626 km2) |  |
| Bent County | 011 | Las Animas | 1870-02-11 | Split from Huerfano County and former Cheyenne and Arapaho tribal land. | Named in honor of frontier trader William Bent. | 5,650 | 1,541.07 sq mi
(3,991 km2) |  |
| Boulder County | 013 | Boulder | 1861-11-01 | Created as one of the 17 original counties of the Territory of Colorado. | Named for the abundance of granite boulders along Boulder Creek. | 330,758 | 740.48 sq mi
(1,918 km2) |  |
| City and County of Broomfield | 014 | Broomfield | 2001-11-15 | 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. | 74,112 | 33.57 sq mi
(87 km2) |  |
| Chaffee County | 015 | Salida | 1879-02-10 | Split from Carbonate County. | Named in honor of Jerome Bunty Chaffee, one of Colorado's first two U.S. Senators from 1876 to 1879. | 19,476 | 1,014.12 sq mi
(2,627 km2) |  |
| Cheyenne County | 017 | Cheyenne Wells | 1889-03-25 | Split from Elbert and Bent counties. | Named for the Cheyenne Nation of Native Americans. | 1,748 | 1,781.90 sq mi
(4,615 km2) |  |
| Clear Creek County | 019 | Georgetown | 1861-11-01 | Created as one of the 17 original counties of the Territory of Colorado. | Named for Clear Creek which originates in the county. | 9,397 | 396.53 sq mi
(1,027 km2) |  |
| Conejos County | 021 | Conejos | 1861-11-01 | 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. | 7,461 | 1,290.22 sq mi
(3,342 km2) |  |
| Costilla County | 023 | San Luis | 1861-11-01 | 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. | 3,499 | 1,229.38 sq mi
(3,184 km2) |  |
| Crowley County | 025 | Ordway | 1911-05-29 | Split from Otero County. | Named in honor of Colorado State Senator John H. Crowley. | 5,922 | 800.27 sq mi
(2,073 km2) |  |
| Custer County | 027 | Westcliffe | 1877-03-09 | 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. | 4,704 | 739.24 sq mi
(1,915 km2) |  |
| Delta County | 029 | Delta | 1883-02-11 | Split from Gunnison County. | Named for the town of Delta located at the delta of the Uncompahgre River. | 31,196 | 1,149.44 sq mi
(2,977 km2) |  |
| City and County of Denver | 031 | Denver | 1902-12-01 | 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. | 715,522 | 155.66 sq mi
(403 km2) |  |
| Dolores County | 033 | Dove Creek | 1881-03-04 | 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. | 2,326 | 1,076.93 sq mi
(2,789 km2) |  |
| Douglas County | 035 | Castle Rock | 1861-11-01 | 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. | 357,978 | 842.30 sq mi
(2,182 km2) |  |
| Eagle County | 037 | Eagle | 1883-02-11 | Split from Summit County. | Named for the Eagle River which originates in the county. | 55,731 | 1,700.76 sq mi
(4,405 km2) |  |
| El Paso County | 041 | Colorado Springs | 1861-11-01 | 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. | 730,395 | 2,128.60 sq mi
(5,513 km2) |  |
| Elbert County | 039 | Kiowa | 1874-02-02 | Split from Douglas County. | Named in honor of Samuel Hitt Elbert, the sixth Governor of the Territory of Colorado. | 26,062 | 1,849.08 sq mi
(4,789 km2) |  |
| Fremont County | 043 | Cañon City | 1861-11-01 | 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. | 48,939 | 1,533.09 sq mi
(3,971 km2) |  |
| Garfield County | 045 | Glenwood Springs | 1883-02-10 | Split from Summit County. | Named in honor of James Abram Garfield (1831 - 1881), the twentieth President of the United States. | 61,685 | 2,958.23 sq mi
(7,662 km2) |  |
| Gilpin County | 047 | Central City | 1861-11-01 | 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. | 5,808 | 150.15 sq mi
(389 km2) |  |
| Grand County | 049 | Hot Sulphur Springs | 1874-02-02 | 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. | 15,717 | 1,868.53 sq mi
(4,839 km2) |  |
| Gunnison County | 051 | Gunnison | 1877-03-09 | Split from Lake County. | Named in honor of John Williams Gunnison, the U.S. Army captain who explored the region. | 16,918 | 3,259.22 sq mi
(8,441 km2) |  |
| Hinsdale County | 053 | Lake City | 1874-02-10 | Split from Lake, Conejos, and Costilla counties. | Named in honor of George Aaron Hinsdale, a Lieutenant Governor of the Territory of Colorado. | 788 | 1,123.35 sq mi
(2,909 km2) |  |
| Huerfano County | 055 | Walsenburg | 1861-11-01 | 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. | 6,820 | 1,592.37 sq mi
(4,124 km2) |  |
| Jackson County | 057 | Walden | 1909-05-05 | Split from Larimer County. | Named in honor of Andrew Jackson (1767 - 1845), the seventh President of the United States. | 1,379 | 1,619.75 sq mi
(4,195 km2) |  |
| Jefferson County | 059 | Golden | 1861-11-01 | 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. | 582,910 | 772.85 sq mi
(2,002 km2) |  |
| Kiowa County | 061 | Eads | 1889-04-11 | Split from Bent County. | Named for the Kiowa Nation of Native Americans. | 1,446 | 1,785.90 sq mi
(4,625 km2) |  |
| Kit Carson County | 063 | Burlington | 1889-04-11 | Split from Elbert County. | Named in honor of Christopher Houston "Kit" Carson, the famous frontier scout and soldier. | 7,087 | 2,162.43 sq mi
(5,601 km2) |  |
| La Plata County | 067 | Durango | 1874-02-10 | Split from Lake and Conejos counties. | Named for the many silver deposits in the area. La plata is a Spanish expression for the silver. | 55,638 | 1,700.44 sq mi
(4,404 km2) |  |
| Lake County | 065 | Leadville | 1861-11-01 | 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. | 7,436 | 383.55 sq mi
(993 km2) |  |
| Larimer County | 069 | Fort Collins | 1861-11-01 | Created as one of the 17 original counties of the Territory of Colorado. | Named in honor of William Larimer, a pioneer entrepreneur. | 359,066 | 2,631.75 sq mi
(6,816 km2) |  |
| Las Animas County | 071 | Trinidad | 1866-02-09 | 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. | 14,555 | 4,773.27 sq mi
(12,363 km2) |  |
| Lincoln County | 073 | Hugo | 1889-04-11 | Split from Elbert and Bent counties. | Named in honor of Abraham Lincoln (1809 - 1865), the sixteenth President of the United States. | 5,675 | 2,585.21 sq mi
(6,696 km2) |  |
| Logan County | 075 | Sterling | 1887-02-25 | Split from Weld County. | Named in honor of John Alexander Logan (1826 - 1886), a U.S. Army general and U.S. Senator from Illinois. | 21,528 | 1,845.31 sq mi
(4,779 km2) |  |
| Mesa County | 077 | Grand Junction | 1883-02-14 | Split from Gunnison County. | Named for the mesa formations which are widespread through the area. | 155,703 | 3,345.69 sq mi
(8,665 km2) |  |
| Mineral County | 079 | Creede | 1893-03-27 | Split from Hinsdale, Rio Grande, and Saguache counties. | Named from the plentiful mineral deposits found in the area. | 865 | 878.16 sq mi
(2,274 km2) |  |
| Moffat County | 081 | Craig | 1911-02-27 | Split from Routt County. | Named in honor of railroad pioneer David H. Moffat. | 13,292 | 4,755.86 sq mi
(12,318 km2) |  |
| Montezuma County | 083 | Cortez | 1889-04-16 | Split from La Plata County. | Named in honor of Aztec leader Moctezuma II. Ruins in the area were once thought to be Aztec. | 25,849 | 2,035.80 sq mi
(5,273 km2) |  |
| Montrose County | 085 | Montrose | 1883-02-11 | 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. | 42,679 | 2,246.43 sq mi
(5,818 km2) |  |
| Morgan County | 087 | Fort Morgan | 1889-02-19 | Split from Weld County. | Named for old Fort Morgan, which in turn was named in honor of U.S. Army Colonel Christopher A. Morgan. | 29,111 | 1,293.83 sq mi
(3,351 km2) |  |
| Otero County | 089 | La Junta | 1889-03-25 | Split from Bent County. | Named in honor of Miguel A. Otero of the prominent Otero family of the Southwest. | 18,690 | 1,267.66 sq mi
(3,283 km2) |  |
| Ouray County | 091 | Ouray | 1877-01-18 | 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. | 4,874 | 542.30 sq mi
(1,405 km2) |  |
| Park County | 093 | Fairplay | 1861-11-01 | Created as one of the 17 original counties of the Territory of Colorado. | Named for South Park which occupies most of the county. | 17,390 | 2,209.36 sq mi
(5,722 km2) |  |
| Phillips County | 095 | Holyoke | 1889-03-27 | Split from Logan County. | Named in honor of R.O. Phillips, secretary of the Lincoln Land Company, which sold farmsteads in the area. | 4,530 | 688.30 sq mi
(1,783 km2) |  |
| Pitkin County | 097 | Aspen | 1881-02-23 | Split from Gunnison County. | Named in honor of Frederick Walker Pitkin, the second Governor of the State of Colorado. | 17,358 | 970.37 sq mi
(2,513 km2) |  |
| Prowers County | 099 | Lamar | 1889-04-11 | Split from Bent County. | Named in honor of John W. Prowers, a pioneer of the Arkansas River valley. | 11,999 | 1,645.37 sq mi
(4,261 km2) |  |
| Pueblo County | 101 | Pueblo | 1861-11-01 | 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. | 168,162 | 2,396.77 sq mi
(6,208 km2) |  |
| Rio Blanco County | 103 | Meeker | 1889-03-25 | Split from Garfield County. | Named for the White River, which was originally named Rio Blanco in Spanish. | 6,529 | 3,226.24 sq mi
(8,356 km2) |  |
| Rio Grande County | 105 | Del Norte | 1874-02-10 | Split from Costilla County and Conejos County counties. | Named for the Rio Grande, which flows through the area. | 11,539 | 913.10 sq mi
(2,365 km2) |  |
| Routt County | 107 | Steamboat Springs | 1877-01-29 | Split from Grand County. | Named in honor of John Long Routt, the first Governor of the State of Colorado. | 24,829 | 2,362.11 sq mi
(6,118 km2) |  |
| Saguache County | 109 | Saguache | 1866-12-29 | Split from Lake and Costilla counties. | Name comes from a Ute language noun meaning "sand dunes".[b] [9] | 6,368 | 3,168.32 sq mi
(8,206 km2) |  |
| San Juan County | 111 | Silverton | 1876-01-31 | Split from Lake County. | Named for the San Juan River and San Juan Mountains, which in turn were named for Saint John the Evangelist. | 705 | 388.99 sq mi
(1,007 km2) |  |
| San Miguel County | 113 | Telluride | 1883-03-02 | 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. | 8,072 | 1,290.76 sq mi
(3,343 km2) |  |
| Sedgwick County | 115 | Julesburg | 1889-04-09 | Split from Logan County. | Named for Fort Sedgwick, which, in turn, was named for U.S. Army General John Sedgwick (1813 - 1864). | 2,404 | 548.83 sq mi
(1,421 km2) |  |
| Summit County | 117 | Breckenridge | 1861-11-01 | Created as one of the 17 original counties of the Territory of Colorado. | Named for the many high mountain summits in the area. | 31,055 | 618.92 sq mi
(1,603 km2) |  |
| Teller County | 119 | Cripple Creek | 1899-03-23 | 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. | 24,710 | 558.58 sq mi
(1,447 km2) |  |
| Washington County | 121 | Akron | 1887-02-09 | Split from Weld County. | Named in honor of George Washington (1732 - 1799), the first President of the United States. | 4,817 | 2,522.90 sq mi
(6,534 km2) |  |
| Weld County | 123 | Greeley | 1861-11-01 | 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. | 328,981 | 4,013.84 sq mi
(10,396 km2) |  |
| Yuma County | 125 | Wray | 1889-03-15 | Split from Washington County. | Named for the Quechan (Yuma) Nation of Native Americans. | 9,988 | 2,369.61 sq mi
(6,137 km2) |  |