The three-years 4th Ohio Infantry was organized at Camp Dennison on June 4, 1861. After a few days of training and drilling, it moved to Grafton, Virginia (now West Virginia) on June 20–23, where it was attached to Alexander M. McCook's Advance Brigade, West Virginia, until July. 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. They remained on duty in western Virginia through the balance of the year, fighting in several small skirmishes and battles.