|Country United States|
|Active August 31, 1861 to July 24, 1865|
Engagements Battle of Secessionville Second Battle of Bull Run Battle of Chantilly Battle of South Mountain Battle of Antietam Battle of Fredericksburg Siege of Vicksburg Siege of Jackson Knoxville Campaign Rapidan Campaign Battle of the Wilderness Battle of Spotsylvania Court House Battle of North Anna Battle of Totopotomoy Creek Battle of Cold Harbor Siege of Petersburg Battle of the Crater Battle of Globe Tavern Battle of Boydton Plank Road Battle of Fort Stedman Appomattox Campaign Third Battle of Petersburg
The 100th Pennsylvania Volunteer Infantry ("The Roundheads" and "The Round Head Regiment") was an infantry regiment that served in the Union Army during the American Civil War.
The 100th Pennsylvania Infantry was organized at Pittsburgh, Pennsylvania and mustered in August 31, 1861 for a three-year enlistment under the command of Colonel Daniel Leasure.
The regiment was attached to Stevens' 2nd Brigade, Sherman's South Carolina Expedition, to April 1862. 2nd Brigade, 2nd Division, Department of the South, to July 1862. 2nd Brigade, 1st Division, IX Corps, Army of the Potomac, to September 1863. 3rd Brigade, 1st Division, IX Corps, to April 1863. 3rd Brigade, 1st Division, IX Corps, Department of the Ohio, to June 1863. Army of the Tennessee, to August 1863, and Army of the Ohio, to March 1864. 2nd Brigade, 1st Division, IX Corps, Army of the Potomac, to June 1864. 1st Brigade, 1st Division, IX Corps, to September 1864. 3rd Brigade, 1st Division, IX Corps, to July 1865.
The 100th Pennsylvania Infantry mustered out July 24, 1865.
Left Pennsylvania for Washington, D.C., September 2, and duty there until October 9. Moved to Annapolis, Md., October 9. Sherman's Expedition to Port Royal Harbor, S.C., October 21-November 7, 1861. Capture of Forts Walker and Beauregard, Port Royal Harbor, November 7. Occupation of Beaufort, S.C., December 8, and duty there until June 1862. Port Royal Ferry, Coosa River, January 1. Operations on James Island, S.C., June 1-28. Legaire's Point, James Island, June 3. Skirmishes on James Island June 3-4. Battle of Secessionville, James Island, June 16. Evacuation of James Island and movement to Hilton Head, S.C., June 28-July 7. Moved to Newport News, Va., July 12-17, then to Fredericksburg August 4-6. Operations in support of Pope August 6-16. Pope's Campaign in northern Virginia August 16-September 2. Battle of Groveton August 29. Second Battle of Bull Run August 30. Battle of Chantilly September 1. Maryland Campaign September 6-24. Battle of South Mountain September 14. Battle of Antietam September 16-17. Marched up the Potomac River to Leesburg, then to Falmouth October 11-November 18. Battle of Fredericksburg December 12-15. Burnside's 2nd Campaign, "Mud March," January 20-24, 1863. Moved to Newport News, Va., February 13, then to Covington, Ky., March 20-28. Duty in District of Kentucky. At Paris, Nicholasville, Lancaster, Stanford, and Somerset until June. Movement through Kentucky to Cairo, Ill., June 4-10, then to Vicksburg, Miss., June 14-17. Siege of Vicksburg June 17-July 4. Advance on Jackson, Miss., July 5-10. Siege of Jackson July 10-17. Duty at Milldale until August 6. Moved to Covington, Ky., then to Crab Orchard, Ky., August 6-18. Marched to Knoxville, Tenn., September 10-26, and duty there until October 3. Action at Blue Springs October 10. Knoxville Campaign November 4-December 23. Campbell Station November 16. Siege of Knoxville November 17-December 4. Repulse of Longstreet's assault on Fort Saunders November 29. Pursuit of Longstreet December 5-24. At Blain's Cross Roads until January 1864. Veterans marched over the Cumberland Mountains to Nicholasville, Ky., January, and on furlough until March. Ordered to Annapolis, Md., and duty there until April. Rapidan Campaign May 4-June 12. Battle of the Wilderness May 5-7. Spotsylvania May 8-12. Ny River May 10. Spotsylvania Court House May 12-21. Assault on the Salient May 12. North Anna River May 12-21. Ox Ford May 24. Line of the Pamunkey May 26-28. Totopotomoy May 28-31. Cold Harbor June 1-12. Bethesda Church June 1-3. Before Petersburg June 16-18. Siege of Petersburg June 16, 1864 to April 2, 1865. Mine Explosion, Petersburg, July 30, 1864. Weldon Railroad August 18-21. Poplar Springs Church September 29-October 2. Reconnaissance on Vaughan and Squirrel Level Road November 8. Boydton Plank Road, Hatcher's Run, October 27-28. Fort Stedman March 25, 1865. Appomattox Campaign March 28-April 9. Assault on and fall of Petersburg April 2. Occupation of Petersburg April 3. Pursuit of Lee April 3-8. Moved to Washington, D. C, April 21-28, and duty there until July. Grand Review of the Armies May 23.
The regiment lost a total of 409 men during service; 16 officers and 208 enlisted men killed or mortally wounded, 2 officers and 183 enlisted men died of disease.