County Down is one of six counties that form Northern Ireland in the northeast of the island of Ireland. Along the southeast shore of Lough Neagh, it covers an area of 2,448 km² (945 sq mi) and has a population of 531,665. It is also one of the thirty-two traditional counties of Ireland and is within the province of Ulster. 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 town is Bangor, on the northeast coast. Three other large towns and cities are on its border: Newry lies on the western border with County Armagh, while Lisburn and Belfast lie on the northern border with County Antrim. Down contains both the southernmost point of Northern Ireland (Cranfield Point) and the easternmost point of Ireland (Burr Point).

Newcastle is often called the Jewel in Crown for Newry Mourne and Down Council. Newcastle is a seaside resort in County Down, Northern Ireland, which had a population of 7,444 at the 2001 Census. It lies on the Irish Sea at the foot of Slieve Donard, one of the Mourne Mountains, and is known for its sandy beach and the Royal County Down Golf Club.

The town aims to promote itself as the “activity resort” for Northern Ireland and its most special attribute is its location at the foot of Slieve Donard. The town has benefited from a multi million upgrade which makes it a high quality seaside attraction. The town is twinned with New RossCounty Wexford, in the Republic of Ireland.