The 20th Illinois Infantry was organized at
Joliet, Illinois, and mustered into Federal service on June 13, 1861, for a three-year enlistment. The regiment spent its first months of service in Missouri, establishing a base near Cape Girardeau. On October 20, 1861, the regiment saw its first engagement at
Fredericktown, where it was actively engaging the Confederate forces there.
Battles in Tennessee In February 1862, the regiment was assigned to Wallace's Brigade of
McClernand's Division. They took part in the
Battle of Fort Henry and later, the
Battle of Fort Donelson. Following the Confederate surrender, the regiment moved to Pittsburg Landing. On April 6–7, 1862, the 20th Illinois Fought in the
Battle of Shiloh, yet again under McClernand's Division. After the Battle, it took part in the
Siege of Corinth. The regiment spent the summer of 1862 conducting garrison duty in
Jackson, Tennessee, and guarding the Mobile and Ohio Railroad. On September 1, 1862, the regiment fought in the
Battle of Britton's Lane, Relieving Union troops at Medon Station.
Vicksburg Campaign In early 1863, the regiment took part in the
Vicksburg Campaign, where it was attached to the First Brigade, Logan's Division,
XVII Corps. They participated in a series of battles that isolated the city, which were
Port Gibson,
Raymond,
Champion Hill, and
Big Black River Bridge. During the
Siege of Vicksburg, the 20th Illinois occupied a position on the Jackson Road and participated in major assaults on May 19, 22, and June 25. The regiment entered the city upon its surrender on July 4, 1863. In early 1864, a majority of the regiment were re-enlisted as veterans and returned to Illinois for a 30-day furlough. By June 1864, they joined Sherman's Army for the
Atlanta Campaign. The regiment was heavily engaged at
Kennesaw Mountain and
Atlanta. During the fierce fighting, the regiment was positioned on the extreme left flank of the army; during the Confederate assault, many members of the regiment were surrounded and captured.
March to the Sea and the Carolinas Campaign After the fall of Atlanta, the 20th Illinois joined
Sherman's March to the Sea, entering Savannah on Christmas Day, 1864. In January 1865, they joined in the
Carolinas Campaign, participating in the
Battle of Bentonville. Following the Surrender of Joseph E. Johnston's Army at Raleigh, the regiment marched north to Washington, D.C., Where it took part in the
Grand Review of the Armies on May 24, 1865. The Regiment moved to Louisville Kentucky, where it was mustered out of Service on July 16, 1865. The regiment was mustered out of service on July 16, 1865. ==Total strength and casualties==