The 4th Ohio Infantry Regiment was organized April 25, 1861, at Camp Jackson in Columbus, with Lorin Andrews as its colonel.
As part of the 3rd Brigade, Army of Occupation, the regiment saw action in the West Virginia Campaign, capturing the Confederate-held town of Beverly on July 12.
Brigaded with the 7th West Virginia, 14th Indiana, and 8th Ohio Infantry under Nathan Kimball in the II Corps, the regiment was briefly stationed in Fort Monroe before covering John Pope's retreat from the Second Battle of Bull Run on September 1.
Then it was part of the infamous January "Mud March," one of Ambrose Burnside's follies as the commanding general of the Army of the Potomac.
They arrived in time to help repulse the Louisiana Tigers of Harry Hays, who had seized several Union artillery pieces.
After a series of smaller engagements, the 4th was a part of an ill-advised charge against Confederate entrenchments at the futile Battle of Cold Harbor in June.
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.