J. Henry Denig was born on September 8, 1838, in York, Pennsylvania. He enlisted in the U.S. Marine Corps on June 6, 1861, at Philadelphia, Pennsylvania, and served aboard the sloop-of-war USS Brooklyn during the U.S. Civil War. Sgt Denig was awarded the Medal of Honor for his actions aboard USS Brooklyn during the Battle of Mobile Bay on August 5, 1864, and he received an honorable discharge from the Marine Corps on September 8, 1864. Henry Denig died on December 10, 1876, and was buried at the Prospect Hill Cemetery in York, Pennsylvania.
His Medal of Honor Citation reads:
On board the U.S.S. BROOKLYN during action against rebel forts and gunboats and with the ram TENNESSEE, in Mobile Bay, 5 August 1864. Despite severe damage to his ship and the loss of several men on board as enemy fire raked her decks, Sergeant Denig fought his gun with skill and courage throughout the furious 2-hour battle which resulted in the surrender of the real ram TENNESSEE and in the damaging and destruction of batteries at Fort Morgan.