The 11th Regiment Illinois Volunteer Infantry was an infantry regiment from Illinois that served in the Union Army during the American Civil War. In April 1861, it was formed as a three-month volunteer unit, and in July 1861 it was reorganized as a three-year unit, in which role it served until the end of the war. Two of its commanding officers were promoted to brigadier general and led major units during the war. In its first major action at Fort Donelson the regiment suffered terrible losses. The 11th Illinois also fought at Shiloh, Riggins Hill, Vicksburg, First Yazoo City, Second Yazoo City, and Fort Blakely. In April 1863, the 109th Illinois Infantry Regiment was disbanded and its enlisted men transferred into the 11th Illinois. The regiment was mustered out of service in July 1865.