The 10th Maine Infantry Regiment was mustered in for two years of service at Portland, Maine, on October 4, 1861, by then-Major Seth Eastman. It was mustered out on May 8, 1863, also at Portland. The regimental commander was Colonel George Lafayette Beal. The 10th Maine was a re-organization of the 1st Maine Infantry, a regiment primarily composed of men with two-year enlistments that was mustering out after completing three months of Federal service. Eight companies of the 1st Maine were retained in service, with Companies A and D replaced by newly recruited companies.