Originally a three months regiment, but reorganized for the three years service on September 20, 1861. It moved into Kentucky on the same day, being the first body of troops to enter that State from the North. Having been assigned to Rousseau's Brigade of McCook's Division, it remained in Kentucky until March, 1862, when it marched to Pittsburg Landing, Tenn., arriving there in time to participate in the second day's battle at Shiloh, where it rendered effective service. Its loss in this, its first battle, was 4 killed, 36 wounded, and 2 missing. The regiment fought next at Stone's River, — then in Johnson's (1st) Division of McCook's Corps, Colonel Baldwin commanding the brigade, and Lieutenant-Colonel Tripp the regiment; its casualties on that field were 17 killed, 50 wounded, and 37 missing. The regiment remained at Murfreesboro until June, 1863, when it marched with Rosecrans on his advance to Chattanooga and successful occupation of that place. Colonel Baldwin was killed at Chickamauga while in command of the brigade, the regiment losing there 13 killed, 116 wounded, and 312 missing. Upon the reorganization of the Army of the Cumberland in October, 1863, it became a part of Hazen's (2d) Brigade, Wood's (3d) Division, Fourth Corps, in which command it took part in the storming of Missionary Ridge, where it sustained a heavy loss (76) in proportion to the small number engaged. The Sixth was engaged in all the battles of the Fourth Corps during the Atlanta campaign, its hardest fighting occurring at Pickett's Mills, where it again suffered a severe percentage of loss. After the Atlanta campaign the regiment was mustered out on September 22, 1864, and the recruits were transferred to the Sixty-eighth Regiment.