The old members of the regiment (the remainder of the original three-years men) mustered out June 21, 1864, and what was left of the 4th Regiment, Ohio Volunteer Infantry was consolidated to a battalion five days later. The much depleted 4th saw action in a series of engagements near Petersburg, including Deep Bottom, Ream's Station, and Hatcher's Run. They served in the Appomattox Campaign from March 28 – April 9, seeing their final major combat in the triumph at the Battle of Sayler's Creek. The victorious army marched to Washington, D.C. in early May, then participated in the Grand Review on May 23. The 4th Ohio mustered out July 12, 1865, in Columbus.