John Couhig was born in Ireland in 1835. He immigrated to America, arriving on April 26, 1855, at age 20-years-old. On May 13, 1861, he enlisted with the New York 79th Infantry, Company I. He was mustered in as a Private on May 28, 1861.

Early in 1862, John took part in the expedition to Port Royal Ferry in January 1862. At some point, John was injured and ended up at a Union hospital in Beaufort, South Carolina, where he signed his name on a plaster wall (see the photo in gallery). He wrote on the wall that he was from Staten Island.

John was apparently well enough to be released. On September 17, 1862, John was killed at the Battle of Antietam. During the Battle of Antietam, the New York 79th led the advance of Christ's Brigade as skirmishers, on the right of the IX Corps line. On the afternoon of September 17th, they were along the bridge road toward Sharpsburg on the Sherrick farm.