The Twelfth Wisconsin Infantry Regiment was organized at Camp Randall, Madison, WI, in October and November 1861. The regiment left the state January 11, 1862, proceeding to Fort Leavenworth, KS, where it remained in active service until the latter part of May. Leaving on the 29th of that month for Columbus, KY, it arrived June 2, 1862, and thereafter the Twelfth was a part of the Army of the Tennessee.

The Twelfth was assigned to the duty of guarding railways and in accompanying expeditions, including the expedition to Coldwater River, MS, April 18-24, 1863. It took part in action at Hernando, MS, April 18, 1863. On the 11 of May it embarked at Memphis, TN, for Vicksburg, MS, and joined in the line of investment of and siege of Vicksburg, June 11, remaining in the trenches until the surrender of that place July 4, 1863. It participated in the Jackson, MS Campaign July 5-25, 1863, and returned to Vicksburg. On the 15 of August the regiment embarked for Natchez, MS, where it remained until November 22 and from this place participated in various expeditions. From February 3-March 6, 1864, it took part in the Meridian Expedition and joined the Army of the Tennessee with General Sherman's forces near Acworth, GA, June 8, 1864. It continued with that Army throughout the Atlanta, the Savannah and the Carolinas Campaigns, serving with Sherman's forces until the surrender of Johnston, April 26, 1865.

The Twelfth then took part in the Grand Review at Washington, D.C. In addition to the actions mentioned above and many minor engagements, the Twelfth participated in the battle of Atlanta, July 21, 1864, and Jonesborough,GA August 31-September 1, 1864. The Twelfth was designated as one of the "Marching Regiments." Its service began with many miles of marching in Kansas, thence transferred to Western Kentucky, Tennessee and Mississippi and finally with Gen. Sherman. It is claimed that the regiment marched 3,838 miles, traveled by railroad 2,506 miles, by steamboat 3,159 miles, a total of 9,503 miles. After the Grand Review, the regiment was sent to Louisville, KY where it went into camp. It was mustered out of service July 16, returned to Madison, WI, and was disbanded August 9, 1865.