[1][2] The 123rd Ohio Infantry was organized at Camp Monroeville in Huron County, Ohio, and mustered in for three years service on September 24, 1862, under the command of Colonel William Tecumseh Wilson.
The regiment was attached to Railroad Division, West Virginia, to January 1863.
Defenses of the Upper Potomac, VIII Corps, Middle Department, to March 1863.
McReynolds' Command, Martinsburg, West Virginia, to December 1863.
3rd Brigade, 1st Division, Department of West Virginia, to April 1864.
1st Brigade, 1st Infantry Division, West Virginia, to December 1864.
Duty at Romney January 10 to March 4, and at Winchester, Va., until June.
Regiment surrendered by Colonel Ely, Commanding Brigade, June 15, 1863.
Duty along Baltimore & Ohio Railroad from Harper's Ferry to Monocacy Junction until April.
Moved to Washington, D.C., December 19; then to Aikens' Landing, Va.