The 11th Regiment Illinois Volunteer Infantry was an infantry regiment that served in the Union Army during the American Civil War. It was originally formed as a three-month volunteer unit at the beginning of the war, and then reorganized as a three-year unit, in which role it served until the end of the war.
The 11th Regiment Illinois Volunteer Infantry disbanded immediately after the Civil War ended.
 It reorganized as a three-year unit, in which role it served until the end of the war; however, nothing is said about when or if it disbanded. The system may confuse the fact it served as a unit until the war's end as meaning it then immediately disbanded.