The 2nd Wisconsin Infantry Regiment was a volunteer infantry regiment that served in the Union Army during the American Civil War. It spent most of the war as a component of the famous Iron Brigade of the Army of the Potomac, and participated in most of the critical battles of the eastern theater of the war, including Antietam, Gettysburg, and Grant's Overland Campaign. It suffered the largest number of casualties as a percentage of its total enlistment of any Union Army unit in the war. The casualties reduced the regiment to an "Independent Battalion" of two companies by July 1864, and the remaining battalion was consolidated into the 6th Wisconsin Infantry Regiment in November 1864.