The 45th Ohio Infantry Regiment was organized at Camp Chase in Columbus, Ohio August 19, 1862, and mustered in for three years service under the command of Colonel Benjamin Piatt Runkle.
The regiment was attached to 3rd Division, Army of Kentucky, Department of the Ohio, September and October 1862.
District of Central Kentucky, Department of the Ohio, to June 1863.
2nd Brigade, 1st Division, XXIII Corps, Department of the Ohio, to July 1863.
3rd Brigade, 1st Division Cavalry Corps, Department of the Ohio, to April 1864.
2nd Brigade, 1st Division, IV Corps, Army of the Cumberland, to June 1865.
The 45th Ohio Infantry mustered out of service at Nashville, Tennessee, on June 12, 1865.
Ordered to Cynthiana, Ky., August 19; then moved to Covington.
Ky., and defense of Cincinnati, Ohio, against threatened attack by Kirby Smith.
Moved to Danville, Ky., January 25, and duty there until March.
Operations in central Kentucky against Cluke's forces February 18-March 5.
Action at Dutton's Hill, near Somerset, March 30.
Expedition to Monticello and operations in southeastern Kentucky April 26-May 12.
Operations against Morgan July 2–26 in response to Morgan's Raid, the 45th, along with Wolford's 1st Kentucky Cavalry and the 2nd Ohio Cavalry, left Jamestown, Kentucky, in pursuit of John Hunt Morgan's troops which had crossed the Cumberland River at Burkesville, Kentucky.
Operations in eastern Kentucky against Scott's forces July 25-August 6.
Burnside's Campaign in eastern Tennessee August 16-October 17.
Operations on line of Pumpkin Vine Creek and battles about Dallas, New Hope Church, and Allatoona Hills May 25-June 5.
Pursuit of Hood to the Tennessee River December 17–28.