List of county seats in Colorado

On August 24, 1859, voters of the Pike's Peak mining region approved the formation of the Provisional Government of the Territory of Jefferson and designated Denver City as the capital.

[2] The extralegal territory was unable to secure authorization from the United States Congress embroiled in the debate over slavery.

On February 28, 1861, after seven slave states seceded from the Union, U.S. President James Buchanan signed An Act to provide a temporary Government for the Territory of Colorado.

[3] On November 1, 1861, the Colorado Territory 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 and Arapaho Reserve.

[4][5] On August 1, 1876, U.S. President Ulysses S. Grant issued Proclamation 230: Admission of Colorado into the Union.

A map showing the location of the U.S. State of Colorado.
The location of the State of Colorado in the United States of America .
A map showing the location of the extralegal Territory of Jefferson in 1859.
The location of the extralegal Territory of Jefferson in the United States of America in 1859.