KILLOUGH (otherwise PORT ST ARNE), a port town of Ireland, situated in the county of Down and province of Ulster, 76 miles from Dublin. It lies north of St John's Point, and has a good quay, where ships lie very safe. The town is agreeably situated, the sea flowing all along the backs of the houses, where ships ride in full view of the inhabitants. There is here a good church, and a horse barrack. They have good fishing in the bay; but the principal trade of the place consists in the exportation of barley, and the importation of such commodities as are consumed in the adjacent country. A manufacture of salt is also carried on with great advantage. The fairs held here are five. At a small distance from the town is a charter working school for the reception of 20 children, which was set on foot by the late Mr Justice Ward. There is a remarkable well here called St Seorain's well, and highly esteemed for the extraordinary lightness of its water. It gushes out of a high rocky bank, close upon the shore, and is observed never to diminish its quantity in the driest season. There is also a mineral spring near the school, the waters of which the inhabitants affirm to be both purgative and emetic. At a small distance from the town near the sea is a rock in which there is an oblong hole, from whence at the ebbing and flowing of the tide a strange noise is heard somewhat resembling the sound of a huntsman's horn. In an open field about a quarter of a mile from the town towards St John's point there is a very curious cave, which has a winding passage two feet and a half broad, with three doors in it besides the entrance, and leading to a circular chamber three yards in diameter, where there is a fine limpid well. The cave is about 27 yards long.