The 11th Pennsylvania Reserves was organized at Camp Wright near Pittsburgh, Pennsylvania[2] beginning May 9, 1861 and mustered in June 29 through July 5, 1861 under the command of Colonel Thomas F. Gallagher.
The regiment was armed with Model 1842 smoothbore muskets and used them for its entire service.
[3] The regiment was attached to 2nd Brigade, McCall's Pennsylvania Reserves Division, Army of the Potomac, to March 1862.
2nd Brigade, 2nd Division, I Corps, Army of the Potomac, to April 1862.
2nd Brigade, McCall's Division, Department of the Rappahannock, to June 1862.
3rd Brigade, 3rd Division, III Corps, Army of Virginia, to September 1862.
3rd Brigade, 3rd Division, I Corps, Army of the Potomac, to February 1863.
3rd Brigade, Pennsylvania Reserves Division, XXII Corps, Department of Washington, to June 1863.
3rd Brigade, 3rd Division, V Corps, Army of the Potomac, to November 1863.
Duty at Tennallytown, Md., and picket at Great Falls August 2 to October 10, 1861.
Duty at Manassas Junction, Catlett's Station, and Falmouth, until June.