The 138th Pennsylvania Volunteer Infantry Regiment lost 6 officers and 90 enlisted men killed or mortally wounded and 1 officer and 70 enlisted men to disease during the Civil War.

It is honored on the Pennsylvania Monument on the Monocacy Battlefield outside Frederick, Maryland.

1862
August 16 Organized at Harrisburg under Colonel C.L.K. Sumwalt, Lt. Colonel M. R. McClennan and Major Lewis A. May
August 30 Moved to Baltimore, Md. then to duty at Relay House. Attached to Relay House, Defenses of Baltimore, 8th Corps, Middle Dept.
1863
February Attached to 3rd Separate Brigade, 8th Corps
March 30 Colonel Sumwalt dismissed.
May 2 Lt. Colonel McClennan promoted to colonel
June 16 Moved to Harper’s Ferry, W. Va. and assigned to Elliott’s Command, 8th Corps
July 1-5 Escort stores to Washington
July 7 Join Division at Frederick, Md. atached to 2nd Brigade, 3rd Division, 3rd Army Corps, Army of the Potomac
July 7-24 Pursuit of Lee
July 23 Wapping Heights
October 9-22 Bristoe Campaign
November 7-8 Advance to line of the Rappahannock
November 7 Kelly’s Ford
November 8 Brandy Station
November 26-December 2 Mine Run Campaign

Colonel McClennan was wounded

November 27 Payne’s Farm
1864
February 6-7 Demonstration on the Rapidan
February Durty at and near Brandy Station
March Attached to 2nd Brigade, 3rd Division. 6th Army Corps, Army of the Potomac
May 4-June 12 Rapidan Campaign
May 5-7 Battle of the Wilderness
May 8-12 Spottsylvania
May 12-21 Spottsylvania Court House
May 12 Assault on the Salient
May 23-26 North Anna River
May 26-28 On line of the Pamunkey
May 28-31 Totopotomoy
June 1-12 Cold Harbor
June 17-18 Before Petersburg
June 22-23 Jerusalem Plank Road, Weldon Railroad
June 24- July 6 Siege of Petersburg
July 6-8 Moved to Baltimore, Md.
July 9 Battle of Monocacy
July 14-24 Pursuit of Early to Snicker’s Gap
August to December Sheridan’s Shenandoah Valley Campaign, asigned to Army of the Shenandoah
August 21-22 Charlestown
September 19 Battle of Opequan, Winchester
September 22 Fisher’s Hill
October 19 Battle of Cedar Creek
October-December Duty at Kernstown
December Moved to Washington, D.C., then to Petersburg, Va. to join siege
1864
February 12 Major May promoted to lieutenant colonel
March 25 Fort Fisher, Petersburg
March 28-April 9 Appomattox Campaign
April 2 Assault on and fall of Petersburg
April 6 Sailor’s Creek
April 9 Appomattox Court House. Surrender of Lee and his army.
April 23-27 March to Danville and duty there
May 23-June 3 March to Richmond, Va. then to Washington, D. C.
June 8 Corps review
June 23 Mustered out under Colonel McClennan and Lt. Colonel May