The 20th Maine Regiment was mustered in at Augusta, Maine, for three years' service on August 29, 1862, and were mustered out on July 16, 1865. Of the 1,621 men enrolled in the regiment, 147 were killed or died of wounds, 146 died of disease, and 15 were in Confederate prisons.

They served in the following engagements:

• Antietam, MD - September 17, 1862
• Shepherdstown Ford, VA - September 19 - 20, 1862
• Fredericksburg, VA - December 13, 1862
• Chancellorsville, VA - May 1 - 4, 1863
• Middleburg, VA - June 17, 1863
• Gettysburg, PA - July 1 - 3, 1863
• Sharpsburg Pike, MD - July 1863
• Rappahannock Station, VA - November 7, 1863
• Mine Run, VA - November 26 - December 1, 1863
• Wilderness, VA - May 5 - 7, 1864
• Spotsylvania, VA - May 7 - 20, 1864
• North Anna, VA - May 23 - 27, 1864
• Totopotomy, VA - May 26, - 30, 1864
• Bethesda Church, VA - May 30 - June 1, 1864
• Cold Harbor, VA - May 31 - June 12, 1864
• Petersburg, VA - June 1864
• Jerusalem Plank Road, VA - June 22 - 23, 1864
• Weldon Railroad, VA - August 18 - 21, 1864
• Peebles Farm, VA - September 30 - October 2, 1864
• Hatchers Run, VA - December 8 - 9, 1864
• Quaker Road, VA - March 29, 1865
• Gravelly Run, VA - March 29, 1865
• Five Forks, VA - March 30 - April 1, 1865
• Appomattox, VA - March 29 - April 9, 1865