Mustered in originally as a three months regiment. It was remustered at Bird's Point, Mo., for three years, on July 13, 1861, one-third of the men remaining in the service. The regiment performed garri son duty in Missouri until February, 1862, when it embarked on the campaign against Forts Henry and Donel son. In the storming of Fort Donelson it lost 70 killed, 181 wounded, and 88 missing; a total of 339 out of about 500 engaged; many of the missing were killed or wounded. The regiment was then m W. H. Wallace's Brigade of McClernand's Division. At Shiloh, it fought in Marsh's (2d) Brigade of the same division, taking 239 officers and men into action, and losing 17 killed, 69 wounded, and 17 missing; total, 103. During the Vicksburg campaign it was in Ransom's (2d) Brigade, McArthur's Division, Seventeenth Corps. In the assault on Vicksburg, May 22, 1863, it lost 3 killed, 30 wounded, and 9 missing; Colonel Nevins was among the killed. At Liverpool Heights, February 5, 1864, it lost 4 killed and 9 wounded; at Yazoo City, March 5th, 9 killed, 24 wounded, and 12 missing. In July, 1864, it marched with General Slocum's Expedition against Jackson, Miss. On July 29, 1864, it moved to Morganzia, La., and m March, 1865. it was engaged m the siege operations about Mobile, and in the fighting at Fort Blakely. In April, 1863, the One Hundred and Ninth Illinois was discon tinued, and the men, numbering 589 (on the rolls), were transferred to the ranks of the Eleventh. The Eleventh was mustered out July 14, 1865, and the men with unexpired terms of enlistment were transferred to the Eighth and Forty-sixth Regiments, Illinois Infantry.