Charlemont Fort was a garrison built in Charlemont, County Armagh in 1602 by Lord Mountjoy. It was destroyed in 1920 by fire and the only building remaining today is the gatehouse. The name Charlemont came from Charles Blount's Christian name. It was situated on the Armagh bank of the River Blackwater, it was armed with 150 men under the command of Sir Toby Caulfield, whose descendants took the name Charlemont from the place.
The Stronghold of Charlemont proved to be of great strategic importance in the Irish Confederate Wars in the 1640s, as it was one of only a handful of modern fortresses to be found in Ireland at that time. It was captured by the forces of Felim O'Neill in 1641 and the Ulster army of the Irish Confederates managed to hold onto the fort throughout the 1640s. It was eventually captured by Charles Coote after he had been reinforced by New Model Army soldiers in late 1650, but hundreds of Cootes soldiers were killed in the effort.
The governor's house within the fort, which ceased to be a public building in the mid 19th Century, later became the home of the Charlemonts.
On 30 July 1920 a group of around forty armed men seized the fort, which was being occupied by a caretaker, and burned it down. The ruins were sold in 1921 to a masonry contractor. In 1920 the family also lost their great house Roxborough Castle, Dungannon County Tyrone to the same fate.