The 78th Ohio Infantry was organized at Camp Gilbert in Zanesville, Ohio October 1861 through January 1862 and mustered in for three years service on January 11, 1862, under the command of Colonel Mortimer Dormer Leggett.
The regiment was attached to 2nd Brigade, 3rd Division, District of West Tennessee, to March 1862.
3rd Brigade, 3rd Division, Army of the Tennessee, to July 1862.
Unattached, District of Jackson, Tennessee, to November 1862.
2nd Brigade, 3rd Division, Right Wing, XIII Corps, Department of the Tennessee, to December 1862.
2nd Brigade, 3rd Division, XVII Corps, Army of the Tennessee, to July 1865.
The 78th Ohio Infantry mustered out of service at Louisville, Kentucky, on July 11, 1865.
Moved to Cincinnati, Ohio, then to Fort Donelson, Tenn., February 11–16.
Expedition toward Purdy and operations about Crump's Landing, Tenn., March 9–14.
Duty at Bethel and Grand Junction until August.
Moved to Memphis, Tenn., January 20, then to Lake Providence, La., February 22, and to Milliken's Bend, La., April 17.
Movement on Bruinsburg and turning Grand Gulf April 25–30.
Battles of Raymond May 12; Jackson May 14; Champion Hill May 16.
Surrender of Vicksburg July 4, and duty there until February 1864.