Pierre Guy was born at Cornwall Bridge, the son of Pierre Adolphus and Sarah Beaumont (Swift) Guy, and the great-grandson of the Revolutionary War hero General Heman Swift. Guy’s father was a French Canadian immigrant and a jeweler. The family moved to New York City in the 1840s, bringing Sarah’s younger sister, Abby Swift, with them. Guy enlisted at Cornwall in 1861 as a Corporal and was promoted to 1st Sergeant eleven months later. He was taken prisoner at Drewry’s Bluff on May 16, 1864 and spent the next nine months at Andersonville, during which time the army reduced his rank to Private. After the war, Guy returned to Brooklyn and married Frances Moger.