3rd Brigade, 2nd Division, IV Corps (Union Army) of the Cumberland, till October, 1864.

Primarily involved in long marches and skirmishes until Battle of Chickamauga, fighting against the odds.

The 125th then participated in the Battle of Missionary Ridge, and helped to push Braxton Bragg's men away from Chattanooga, Tennessee.

In the spring of 1864, it joined William Tecumseh Sherman in his Atlanta Campaign.

They fought all the way until the end, at the Battle of Jonesborough, and then followed confederate Lt. Gen. John Bell Hood North to Nashville, Tennessee In Colonel Opdycke's brigade, it fought in Battle of Franklin and the union victory at Nashville.