Organized at Camp Butler, August 28, 1861, moving from there three days later to Cairo, where it was assigned to McClernand's Brigade. It was engaged in the battle of Belmont, November 7, 1861, where it sustained a loss of 9 killed, 27 wounded, and 8 missing; Major Thomas McClurken was killed in that action. In February, 1862, the regiment sailed up the Tennessee River with Grant's Army to Fort Henry; after the reduction of that stronghold by the Navy, the regiment, under Colonel Dennis, marched to Fort Donel son, where it took part in the storming of the works. It was then in Oglesby's (1st) Brigade, McClernand's Division, and lost 19 killed, 69 wounded, and 6 missing. The Thirteenth was present at the Siege of Corinth, after which it remained in Northern Mississippi until the opening of the Vicksburg campaign in the spring of 1863, during which time it was engaged in active service, reconnoissances, and frequent encounters with the enemy. In 1863, it served in Leggett's (2d) Brigade, Logan's Division, Seventeenth Corps. It fought under Logan at Champion's Hill, where it lost 9 killed, and 49 wounded. Reenlisting in January, 1864, it went home on the usual furlough, in March, and on its return joined Sherman's Army on June 10th, at Ackworth, Ga. While in Leggett's (3d) Division, Seventeenth Corps, it was hotly engaged in the battle of Atlanta, July 22, 1864, in in which it suffered a severe loss. After the fall of Atlanta, it marched with Sherman to the Sea, and thence on the campaign through the Carolinas in the spring of 1865. It was then in Ewing's (1st) Brigade, Leggett's (3d) Division, Seventeenth Corps.