Colorado became a territory just a few weeks before the firing on Fort Sumter signaled the official beginning of the Civil War. Although sentiments were somewhat divided in the early days of the war, Colorado was a Union territory. A Confederate flag was raised over Denver, nearly sparking a riot, but it was quickly pulled down. Early attempts to enlist Confederate volunteers were also thwarted.
When President Lincoln called for volunteer soldiers to supplement the regular army, Colorado responded. Eventually, nearly 4,000 men from the Colorado Territory served in the volunteer Union forces authorized by the United States War Department. Hundreds more served in militia companies, authorized by the territorial governor, most of which were formed to fight Indians rather than Confederates.
The National Archives Index contains 8467 names of Colorado men, all Union. Because of the reorganization of the troops during the war, and many of the names having alternate spellings and some with initials only, there are many duplicates.