John Mansfield was the 15th Lieutenant Governor of California from 1880 to 1883. He also was an officer in the Union Army during the American Civil War, serving as the last colonel of the 2nd Wisconsin Volunteer Infantry Regiment of the famed Iron Brigade.
Mansfield responded to President Abraham Lincoln's call to arms in 1861 following the secession of the twelve Southern states that comprised the Confederacy. He enlisted in a local Wisconsin company, the Portage Guards, which became a part of the 2nd Wisconsin, initially brigaded under William T. Sherman. Mansfield first saw action at the First Battle of Bull Run. He served at many of the important battles of the Army of the Potomac, including the battles of South Mountain, Antietam, and Gettysburg, where, as the regiment's major, he assumed command of the 2nd Wisconsin after the senior officer, Lucius Fairchild, was shot. He was subsequently promoted to lieutenant colonel and served in the Bristoe and Mine Run Campaigns. As Colonel of the 2nd Wisconsin, he was wounded and captured in May 1864 at the Battle of the Wilderness.
Towards the end of the Civil War, Mansfield became colonel of the 12th Veteran Reserve Corps, a regiment of former soldiers who had reenlisted. In the omnibus promotions in 1866 following the cessation of hostilities, he was brevetted as a brigadier general of volunteers for "gallant and meritorious services during the war," a rank to date from March 13, 1865.