County Down (Irish: Contae an Dúin) is one of the six counties of Northern Ireland, one of the nine counties of Ulster and one of the traditional thirty-two counties of Ireland. It covers an area of 961 sq mi (2,490 km) and has a population of 552,261. It borders County Antrim to the north, the Irish Sea to the east, County Armagh to the west, and County Louth across Carlingford Lough to the southwest.
In the east of the county is Strangford Lough and the Ards Peninsula. The largest settlement is Bangor, a city on the northeast coast. Three other large towns and cities are on its border: Newry lies on the western border with County Armagh. Lisburn and Belfast lie on the northern border with County Antrim. Down contains the southernmost point of Northern Ireland (Cranfield Point) and the easternmost point of Ireland (Burr Point).