The beginning of this infantry unit was organized in Detroit as they mustered into Federal service on September 16, 1861. This regiment was originally a three-month enlistment, and then retained the number of the original 1st Michigan. This regiment was mainly of farmers, businessmen, and young boys that were within the counties of Washtenaw, Wayne, and Jackson in Southeast Michigan.
At Camp Fountain in the summer of 1861, Ann Arbor became the site of the regimental organization. The initial strength of the 1st Michigan infantry was around 960 soldiers and officers. According to Michigan Argus, the local paper in Ann Arbor in September 1861, the following was stated in the paper.
Just like the 7th Michigan, the 1st Michigan also had 10 companies of soldiers, each made up of men from certain locations across the counties. They set out for Virginia on September 7, 1861.