Recruited in La Salle County, and organized at Ottawa, Ill., in August, 1862. The regiment proceeded immediately to Louisville, Ky, where it was uniformed and armed, after which it was assigned to Dumont's Division of Buell's Army. After participating in the Kentucky campaign of that fall, it was stationed at Hartsville, Tenn., where it was attacked, December 6, 1862, by a Confederate brigade under General Morgan. At that time the garrison at Hartsville consisted of three regiments, two companies of cavalry, and a section of light artillery. After a sharp fight in the fields outside the town, the garrison was surrounded and compelled to surrender; the losses of the One Hundred and Fourth amounted to 25 killed, 131 wounded, and 568 captured. The men were immediately released on parole, and the regiment went to Camp Douglass, Chicago, to await notice of exchange, which was received in the spring of 1863. Rejoining the Army of the Cumberland, the regiment was assigned to Beatty's (1st) Brigade, Negley's (2d) Division, Fourteenth Corps. It was engaged at Hoover's Gap, with a slight loss, and then at Chickamauga, where it lost 2 killed, 46 wounded, and 16 missing. In October, the One Hundred and Fourth was assigned to the First Brigade, First Division, Fourteenth Corps, in which it remained without further change; this division was commanded by Johnson, and then by Carlin. The regiment lost at Peach Tree Creek, 16 killed, 29 wounded, and 5 missing; and at Utoy Creek, 5 killed and 18 wounded. It accompanied Carlin's Division on the March through Georgia, and then fought under Carlin in the Carolinas.