Organized at Chicago, July 22, 1861, and left the State, September 21st, proceeding to St. Louis. It served in Missouri until April, 1862, when it was ordered to Corinth. During the siege of that place it was engaged in the affair at Farmington, losing 2 killed, 12 wounded, and 3 missing. After marching through Mississippi, Northern Alabama, and Tennessee, its next battle occurred at Stone's River. It was then in Roberts's Illinois Brigade, Sheridan's (3d) Division, McCook's Corps; loss, 19 killed, 96 wounded, and 46 missing; Colonel Roberts, who was in command of the brigade, was among the killed. At Chickamauga, Major James Leighton was killed, the loss of the Forty-second in that battle amounting to 28 killed, 128 wounded, and 28 prisoners. In October, 1863, it was placed in Harker's (3d) Brigade, Sheridan's (2d) Division, Fourth Corps, in which command it fought at Missionary Ridge; loss, 5 killed and 40 wounded The division was commanded by General John Newton during the Atlanta campaign, and by General Wagner during the Tennessee campaign against Hood. Major D. W. Norton was killed near New Hope Church, Ga., June 3, 1864- The regiment lost at Spring Hill and Franklin, 24 killed, 95 wounded, and 30 missing; at Nashville, 2 killed and 12 wounded. Having reënlisted, it served throughout the war, and at its close accompanied the Fourth Corps to Texas where it was stationed in 1865, as an Army of Occupation.