In 1862, Hobart left the 4th Infantry to accept promotion to Lieutenant Colonel with the newly organized 21st Wisconsin Volunteer Infantry Regiment. The regiment left Wisconsin in September 1862, but Hobart would not rendezvous with them until a month later due to travel time from Louisiana. Before Hobart's arrival, the 21st had marched to join the Army of Ohio, which had been carrying out a defense against the Confederate Heartland Offensive in Kentucky. At the Battle of Perryville the regiment took significant casualties and their commander, Colonel Benjamin Sweet, was wounded.