William F. Fox, Lt. Col. U. S. V., Regimental Losses in the American Civil War, 1861-1865: A Treatise on the extent and nature of the mortuary losses in the Union regiments, with full and exhaustive statistics compiled from the official records on file in the state military bureaus and at Washington

Many of these regiments dropped their synonyms before the war closed, and were known only by their regular title; and, with some, the synonym was never used except on the printed placards of the recruiting officers.

The 9th, 50th, 80th, 87th, 112th, and 118th Regiments also served part of the time as mounted infantry.

Only one vacancy occurred in the list of Illinois regiments; the 121st failed to complete its organization. One regiment, known as the “Mechanics-Fusileers” or 56th Illinois Infantry, organized in November, 1861, to serve three years, was disbanded within four months, and another regiment, subsequently organized, was designated as the 56th Regiment. This latter regiment lost 11 officers and 195 men by the burning of the steamer “General Lyon,” off Cape Hatteras, March 31, 1865.