The 55th Illinois Infantry was organized at Camp Douglas, Chicago, Illinois and mustered into Federal service on October 31, 1861. Training continued at Benton Barracks, Missouri. The 55th was part of Sherman's Yazoo Expedition.

The regiment was mustered out on August 14, 1865.

Total strength and casualties

The regiment suffered casualties including nine officers, 149 enlisted men who were killed in action, or mortally wounded, and two officers and 127 enlisted men who died of disease, for a total of 286 fatalities.

Commanders

Colonel David Stuart - promoted to brigadier general on November 29, 1862, U.S. Senate refused to confirm appointment, resigned April 3, 1863
Colonel Oscar Malmborg.

Branch
Infantry

Engagements
Battle of Shiloh
Siege of Corinth
Vicksburg Campaign
Battle of Chickasaw Bayou
Battle of Fort Hindman (Arkansas Post)
Battle of Snyder's Bluff
Battle of Jackson (MS)
Battle of Champion Hill
Siege of Vicksburg
Battle of Collierville
Third Battle of Chattanooga
Atlanta Campaign
Battle of Resaca
Battle of Kennesaw Mountain
Battle of Atlanta
Battle of Ezra Church
Battle of Jonesborough
Battle of Allatoona Pass
March to the Sea
Battle of Fort McAllister (1864)
Carolinas Campaign
Battle of Bentonville