The 121st Pennsyvania Infantry Regiment lost 5 officers and 104 enlisted men killed or mortally wounded and 2 officers and 64 enlisted men to disease during the Civil War. It is honored by two monuments at Gettysburg.

1861
August 22 – September 5 Organized at Philadelphia
September Moved to Washington, D.C. Camp at Arlington Heights, near Washington
October 1 Moved to Frederick, Md., and join Army of the Potomac. Attached to 1st Brigade. 3rd Division, 1st Corps.
October Duty at Sharpsburg, Md.
October 30-November 19 Movement to Falmouth, Va.
December 12-15
Battle of Fredericksburg
1863
January 20-24 Burnside’s 2nd Campaign, “Mud March”
February-April Duty at Belle Plains
April 27-May 6 Chancellorsville Campaign
April 29-30 Fitzhugh’s Crossing
May 2-5
Battle of Chancellorsville
June 11-July 24 Gettysburg Campaign
July 1-3
Battle of Gettysburg

The regiment was commanded at Gettysburg by Major Alexander Biddle while his cousin, Colonel Chapman Biddle, held temporary brigade command. Colonel Biddle resumed command of the regiment during the battle despite being slightly wounded on July 1.

From the monument on Seminary Ridge at Gettysburg:

Occupied this position, the extreme left of the Union line. July 2d & 3d on Cemetery Ridge. Present at Gettysburg 11 officers and 286 men. Killed died of wounds 20 men. Wounded 5 officers and 33 men. Captured and missing 1 officer and 60 men.

From the monument on Cemetery Ridge at Gettysburg:

Whole number engaged 7 officers 258 enlisted men. Casualties Killed 12 enlisted men.
Wounded 5 officers, 101 enlisted men. Captured and missing 1 officer 60 enlisted men.
Total 179.

July 5-24 Pursuit of Lee
August-October Duty on line of the Rappahannock
October 9-22 Bristoe Campaign
November 7-8 Advance to line of the Rappahannock
November 26-December 2 Mine Run Campaign
November 30 Licking River Bridge
1864
February 6-7 Demonstration on the Rapidan
February-April Duty near Culpeper
March Attached to 3rd Brigade, 4th Division, 5th Army Corps
May 4-June 12 Rapidan Campaign
May 5-7
Battle of the Wilderness
May 8-21
Spottsylvania Court House
May 8 Laurel Hill
May 12 Assault on the Salient
May 23-26 North Anna River
May 25 Jericho Ford
May 26-28 On line of the Pamunkey
May 28-31 Totopotomoy
June 1-12 Cold Harbor
June 1-3 Bethesda Church
June 16-18 Before Petersburg. Start of Siege of Petersburg attached to 1st Brigade, 1st Division. 5th Army Corps
July 30 Mine Explosion, Petersburg (Reserve)
August 18-21 Weldon Railroad
September Attached to 3rd Brigade, 3rd Division, 5th Army Corps
September 29-October 2 Poplar Springs Church, Peeble’s Farm
October 27-28 Boydton Plank Road, Hatcher’s Run
December 7-12 Warren’s Raid on Weldon Railroad
1865
February 5-7 Dabney’s Mills, Hatcher’s Run
March 28-April 9 Appomattox Campaign
March 29 Lewis Farm, near Gravelly Run
March 30-31 White Oak Road
April 1 Five Forks
April 9
Appomattox Court House

Surrender of Lee and his army.

May 1-12 March to Washington, D.C.
May 23 Grand Review
June 2 Mustered out