Infantry regiments formed in Ohio became known as regiments of Ohio Volunteer Infantry. They served for varying lengths of time, averaging one hundred days to three years. In 1864, the governors of several Northern states convinced federal authorities to call up state militia forces for regular military duty.
In the American Civil War, Ohio provided the federal government with 260 regiments of men, including infantry, artillery, and cavalry units. Ohioans also served in several other regiments from other states, most notably from Kentucky, West Virginia, and Massachusetts, as well as in federal units. Almost 330,000 Ohio men, including 5,092 African Americans, served in the Union military during the conflict.
Infantry regiments formed in Ohio became known as regiments of Ohio Volunteer Infantry. They served for varying lengths of time, averaging one hundred days to three years. In 1864, the governors of several Northern states convinced federal authorities to call up state militia forces for regular military duty. The governors believed that these militiamen would free regular soldiers currently serving in forts or guarding other important sites in Northern states for duty with the Union's invading armies in the Confederacy. Hopefully this surge of men, known as Hundred Days' Men, would allow the North to defeat the South in one hundred days or less while keeping Northern states safe from Confederate attack and anti-war unrest.
On May 14, 1864, the 138th Regiment Ohio Volunteer Infantry mustered into service at Camp Dennison, at Cincinnati, Ohio. The men in the regiment were to serve one hundred days. The 138th consisted of Licking County's 5th Regiment Ohio National Guard, Hardin County's 32nd Battalion Ohio National Guard, and one company of Lorain County's 37th Battalion Ohio National Guard.
On May 14, 1864, authorities dispatched the regiment to Washington, DC, traveling via the Baltimore and Ohio Railroad. Upon reaching North Mountain, the 138th disembarked due to an impassable railroad bridge near Harper's Ferry, West Virginia. After a delay of several days, the regiment arrived at Washington on May 22, 1864. Officials placed the 138th in Forts Albany, Craig, and Tillinghast south of the Potomac River. The regiment garrisoned these fortifications until June 5, 1864, when authorities ordered the 138th to White House, Virginia, where the regiment served on guard duty and supervised Confederate prisoners until June 16. The regiment then boarded ships for Bermuda Hundred, Virginia but disembarked at Fort Powhatan on the James River, twenty-five miles away from Bermuda Hundred. The regiment completed the journey on foot, arriving on June 19, and officials assigned the 138th to picket duty at Point of Rocks and Broadway Landing, Virginia. Authorities soon ordered the regiment to the Cherrystone Inlet on Virginia's Eastern Shore, where the 138th garrisoned several communities, including Eastville. The regiment protected telegraph lines connecting Cherrystone to Wilmington, Delaware and also patrolled for Confederate blockade-runners. In late August 1864, the regiment traveled via the Pennsylvania Central Railroad to Camp Dennison, where the 138th mustered out of service on September 1, 1864.
During the 138th Regiment Ohio Volunteer Infantry’s term of service, eight enlisted men perished from disease or accidents, while no soldiers died from wounds received on the battlefield.