The regiment was formed shortly after the outbreak of the
American Civil War by order of
William Gilpin, the first governor of the territory. Recruiters began enlisting men in August 1861, just six months after the organization of the territory. Known as "Gilpin's Pet Lambs" for the involvement of the governor in its formation, the regiment served in the
Western Theater, at first serving in various detachments throughout the territory. The regiment's most notable service came in the
New Mexico Campaign in the spring of 1862, in which they helped repulse the advance of the
Army of New Mexico under
Henry Hopkins Sibley at the battles of
Glorieta Pass and
Peralta. In November 1862, the unit was reorganized along with Companies C and D of the
2nd Colorado Infantry into the
1st Colorado Cavalry. (This was done since the
US War Department believed cavalry would be better in protecting the Western trails and for fighting the various Indian tribes.) The first colonel of the regiment was
John P. Slough, replaced in April 1862 by Major
John Chivington, later chastised for his role as commander of the
3rd Colorado Cavalry in the November 1864
Sand Creek Massacre. There is a group of
reenactors who portray the First Colorado (Company D) in Denver. The unit celebrated 50 years in 2024. == Flags ==