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).
In March 2018, The Sunday Times published its list of Best Places to Live in Britain, including five in Northern Ireland. The list included three in County Down: Holywood, Newcastle, and Strangford.
County Down takes its name from dún, the Irish word for dun or fort, which is a common root in Gaelic place names (such as Dundee, Dunfermline and Dumbarton in Scotland and Donegal and Dundalk in Ireland). The fort in question was in the historic town of Downpatrick, originally known as Dún Lethglaise ("fort of the green side" or "fort of the two broken fetters").
During the 2nd century the region was home to the Voluntii tribe, according to Ptolemy. From the 400s-1177 County Down formed a central part of the kingdom of Ulaid. Ulaid was a frequent target of Viking raids in the eighth and ninth centuries, however fierce local resistance prevented the Norse from setting up permanent settlements in the region. In 1001 a fleet led by Sigtrygg Silkbeard raided much of the region in retribution for the Ulaiden's refusal to offer him sanctuary from Brian Boru the previous year.
The region was invaded by the Normans in 1177. From the 1180s-1600s the region saw waves of English and Scottish immigration. In 1569 the Irish Parliament passed "An Act for turning of Countries that be not yet Shire Grounds into Shire Grounds". In 1570 a commission was issued in pursance of that statute "to survey and make enquiry in the countries and territories ... that are not shire ground, or are doubtful to what shire they belong; to limit and nominate them a shire or county; to divide them into countries, baronies or hundreds, or to join them to any existing shire or barony" "for the countries or territories of Arde,[a] as well this side Blackstafe[b] as the other side, Copelande islands,[c] the Dufferin,[d] Clandeboy,[e] Kilultoghe, the Glynes[f] with the Raughlines,[g] Momerie and Carie,[h] the Rowte M'William (M'Quillan)[i] and all lands between lough Coine[j] and lough Eaghe,[k] and the water of Strangforde and the Banne.[l] To certify their proceedings before the 1st August." The county was privately planted during the Plantation period (16th-17th centuries). During the Williamite War in Ireland (1689–1691) the county was a centre of Protestant rebellion against the rule of the Catholic James II. After forming a scratch force the Protestants were defeated by the Irish Army at the Break of Dromore and forced to retreat, leading to the whole of Down falling under Jacobite control. Later the same year Marshal Schomberg's large Williamite expedition arrived in Belfast Lough and captured Bangor. After laying siege to Carrickfergus, Schomberg marched south to Dundalk Camp, clearing County Down and much of the rest of East Ulster of Jacobite troops.
The county has a coastline along Belfast Lough to the north and Carlingford Lough to the south (both of which have access to the sea). Strangford Lough lies between the Ards Peninsula and the mainland. Down also contains part of the shore of Lough Neagh. Smaller loughs include Lough Island Reavy and Castlewellan Lake near Castlewellan, Clea Lough near Killyleagh, Lough Money and Loughinisland near Downpatrick and, within the Mourne Mountains, Silent Valley Reservoir, Ben Crom Reservoir, Spelga Dam and Lough Shannagh.
The River Lagan forms most of the border with County Antrim. The River Bann also flows through the southwestern areas of the county. Other rivers include the Clanrye and Quoile.
There are several islands off the Down coast: Mew Island, Light House Island and the Copeland Islands, all of which lie to the north of the Ards Peninsula. Gunn Island lies off the Lecale coast. In addition, there are a large number of small islands in Strangford Lough.
County Down is where, in the words of the song by Percy French, "The mountains of Mourne sweep down to the sea", and the area around the granite Mourne Mountains continues to be known for its scenery. Slieve Donard, at 849 m (2,785 ft), is the highest peak in the Mournes, in Northern Ireland and in the province of Ulster. Another important peak is Slieve Croob, at 534 m (1,752 ft), the source of the River Lagan.
Saul, County Down (from the Irish: Sabhall meaning "Barn") – where Saint Patrick said his first eucharist in Ireland
The city of Newry in the south of the county contains St Patrick's (Church of Ireland, 1578), overlooking the city centre from Church street, on the east side of the city, which is considered to be Ireland's first ever Protestant church. The Newry Canal is also the first summit-level canal ever to be built in the British Isles.
The Down County Board administers Gaelic games in the county. Down is the most successful team north of the border in terms of All-Ireland Senior Football Championships won with five (1960, 1961, 1968, 1991 and 1994) in total. In terms of Ulster, they share that accolade with Cavan who also have 5 titles. They currently have four minor All-Ireland titles, twelve Ulster titles and one under 21 all Ireland title (1979). The Ards peninsula is a hurling stronghold.
The Ulster singer Van Morrison has made reference to the County Down in the lyrics to several songs including "Northern Muse (Solid Ground)", "Mystic of the East" and the nostalgic "Coney Island", which names several places and landmarks in the county. Van Morrison also covered "Star of the County Down" with The Chieftains as a part of their collaboration album Irish Heartbeat.
Sam Hanna Bell based his novel of Ulster rural life, December Bride (1951) in the Ards peninsula. A film version of the novel, also called December Bride, was produced in 1990 and released in November 1991.
The Academy award winning short film The Shore (2011) was filmed in and around Killough bay by director/writer Terry George and his daughter Oorlagh. The film starred Ciaran Hynds, Kerry Condon and Connleth Hill.
^Northern Ireland General Register Office (1975). "Table 1: Area, Buildings for Habitation and Population, 1971". Census of Population 1971; Summary Tables(PDF). Belfast: HMSO. p. 1. Archived(PDF) from the original on 23 July 2019. Retrieved 28 August 2019.
^Lee, JJ (1981). "On the accuracy of the Pre-famine Irish censuses". In Goldstrom, J. M.; Clarkson, L. A. (eds.). Irish Population, Economy, and Society: Essays in Honour of the Late K. H. Connell. Oxford, England: Clarendon Press.