Ballycastle, a seaport and watering-place on the north coast of Co. Antrim, Ireland, in the north parliamentary division, situated on a bay of the same name opposite Rathlin Island. Pop. (1901) 1481. It is connected with the Northern Counties (Midland) railway at Ballymoney by the Ballycastle light railway. The town consists of two divisions, about a quarter of a mile apart and connected by a fine avenue. Towards the close of the 18th century Mr Hugh Boyd, obtaining the estate, devoted himself to the extension and improvement of the town, establishing manufactures, endowing charities and building churches; and succeeded in producing a temporary vitality. Upwards of £150,000, including a large government grant, is said to have been expended upon the pier and harbour; but the violence of the sea overthrew the one and the other became filled with sand. To the east of the town are the remains of Bonamargy Abbey, the burial-place of many of the MacDonnell family. The Carey brook, by the side of which the abbey stands, was formerly called the Margy, and on its waters according to tradition dwelt the four children of Lir, changed to swans by their step-mother until St Columba released them from enchantment. (See P. W. Joyce, Old Celtic Romances.) With this well-known romance is connected the wide-spread belief in Ireland of ill-fortune following the killing of a swan.

Coal-seams, formerly extensively worked, and from an unknown period of antiquity, appear in the cliffs towards Fair Head, and the fisheries are important. The coast-scenery and the view from the hill of Knocklayd are notable.