The 31st Wisconsin Infantry Regiment was a volunteer infantry regiment that served in the Union Army during the American Civil War. They served in the western theater of the war, participating in the Atlanta Campaign, Sherman's March to the Sea (Savannah Campaign), and the Carolinas Campaign.
The 31st Wisconsin Infantry was raised as two battalions beginning in September 1862. The first battalion was organized at Prairie du Chien, comprising companies A, B, C, D, E, and F; they were mustered into federal service under a special order of the War Department on October 9, 1862, to guard Confederate prisoners of war in Wisconsin. The second battalion, consisting of companies G, H, I, and K, was raised at Camp Utley in Racine, Wisconsin. Companies A, D, and F were ordered to Camp Randall on November 14, at the same time, companies B, C, and E, and the incomplete companies G, H, I, and K, were set on temporary duty to guard the draft operations in southeast Wisconsin after recent draft riots. On December 20, the companies were reassembled at Racine; they mustered into federal service as the 31st Wisconsin Infantry Regiment on December 24, 1862.
Companies A–F were mustered out on June 20, 1865. Companies G–K followed on July 8, 1865.
The 31st Wisconsin suffered 23 enlisted men killed in action or who later died of their wounds, plus another 3 officers and 86 enlisted men who died of disease, for a total of 112 fatalities.