Coney Island is situated in Lough Neagh 1 mile from Maghery. The island has a 16th-century stone tower which was used by Shane Ó Neill as a lookout post and stronghold. The island was one of O'Neill's major strongholds, but was delivered to Lord Deputy Sir Henry Sydney in 1567, and appears to have continued in use as a fort for a generation at least. At some later point the defences were thoroughly razed. In the 17th and 18th centuries the island was only sporadically occupied.
In the 1890s, Coney Island was bought by James Alfred Caulfield (1830-1913), 7th Viscount Charlemont, supposedly for £150. He lived in Drumcairne, just outside Stewartstown, and bought the island building a summer house in 1895. The Viscount's remains are entombed in the tower on the island.
In 1946 the island was given to the National Trust by Fred Storey.