The 26th Pennsylvania Infantry was organized in Philadelphia, Pennsylvania on April 20, 1861 and mustered on May 27, 1861 for a three-year enlistment under the command of Colonel William F. Small.

Hooker's Brigade, Division of the Potomac, to October 1861.

Grover's Brigade, Hooker's Division, Army of the Potomac, to March 1862.

1st Brigade, 2nd Division, III Corps, Army of the Potomac, to March 1864.

1st Brigade, 4th Division, II Corps, to June 1864.

Veterans and recruits were transferred to the 99th Pennsylvania Infantry.

Moved to the Virginia Peninsula, Siege of Yorktown, April 5-May 4.

White Oak Swamp and Glendale June 30.

Operations on Orange & Alexandria Railroad October 10–12.

Operations at Rappahannock Bridge and Grove Church February 5–7.

Duty on line of the Rapidan River until October.