The Eighth Wisconsin Infantry, known as the Eagle Regiment, was mustered into the service of the United States September 13, 1861, at Camp Randall, Madison, WI. It left the State on October 12th of the same year and proceeded to Pilot Knob, MO, where it was shortly thereafter assigned to duty with various expeditions and engaged in actions in Southeast Missouri prior to the siege of Island No. 10, March 15 to April 8, 1862. While campaigning the Eighth took part in the battle of Fredericktown, MO, October 21, 1861.

In late April of 1862, the Eighth was transferred to Corinth, MS, and participated in the various movements connected with the siege of Corinth and the battles of Farmington, MS, May 9, 1862, and Corinth October 3-4, 1862. In November of that year an army under General Grant was collected at Grand Junction, TN, to advance overland on Vicksburg, in what was known as the Central Mississippi Campaign. After the destruction of the store of supplies at Holly Springs, December 20, 1862, the plan of General Grant was somewhat changed, and operations were thereafter conducted from Memphis on the river. The Eighth reached Young's Point, LA, March 29, 1863, and was actively engaged until the surrender of Vicksburg July 4, 1863, participating in many of the battles prior to the siege. After the fall of Vicksburg it participated in several minor expeditions in northern Mississippi and Louisiana, and was a part of the forces accompanying the Meridian, MS, Campaign March 10-May 22, 1864, and the Red River, LA, Campaign March 10-May 22, 1864. In November of 1864 it was with the forces sent in pursuit of the Confederates under General Price through Arkansas and Missouri.

In the latter part of November was transferred to Nashville, TN, a part of the re-enforcement of the Union Army under General Thomas, and participated in the battle of Nashville December 15-16, 1864-and the pursuit of Hood to the Tennessee River which followed. The Regiment took part in many minor expeditions until February, when it was transferred to New Orleans and attached to the forces which were making the campaign for the reduction of the Confederate defenses at Mobile. It participated in the siege of Spanish Fort and Fort Blakely March 27-April 8, 1865, and in the assault and capture of Fort Blakely April 9 and occupation of Mobile April 11. After the Mobile campaign, the Eighth remained in central Alabama during the summer until the 5th of September, when it was mustered out of the service and proceeded to Madison where it was disbanded.