George Henry Thomas
The 123rd was initially assigned to the Army of the Ohio from September 1862 to November 1862, and then to the Army of the Cumberland from November 1862 to June 1865. The commanding general of the Army of the Cumberland was William Rosecrans. The regiment was in the 1st Brigade with Colonel Albert S. Hall, which was part of the 5th Division commanded by Brigadier General Joseph J. Reynolds, reporting to Major General George Henry Thomas.