It was organized at Camp Berry in Concord and mustered in on August 23, 1861, for three years service, 1,047 officers and men. The regiment served most of its time on the Atlantic coast in the Carolinas. The 3rd New Hampshire finished the war in North Carolina and were mustered out of Federal service on July 20, 1865, arriving back in Concord on the 28th for final discharge and payment. The 3rd had a total of 198 casualties, with another 154 dying in Confederate prisons, disease, or warfare-related accidents.