Armagh district is located south of Lough (lake) Neagh and is bordered by the districts of Dungannon to the northwest, Craigavon to the northeast, Banbridge to the east, Newry and Mourne to the southeast, and the Republic of Ireland to the southwest. Southern Armagh district is rugged terrain that slopes gradually down to more fertile lowlands in the north. Northern Armagh district is the main fruit-growing region on the island of Ireland, and the villages of Richhill and Loughgall are market centres for apples and strawberries. Light industrial centres include Keady, Laurelvale, and Tanderagee in addition to Armagh city. Most of the formerly important linen mills in the district have closed or diversified into the production of synthetic fibres. Southern Armagh district and adjacent areas near the Irish republic's border were continuing hotbeds of sectarian violence during the late 20th century. Area district, 261 square miles (676 square km). Pop. (2001) city, 14,590; (2004 est.) district, 54,876.

In late prehistoric times and at the dawn of history, Armagh was an important populated area in Ulster. At the beginning of the Christian era, the fortress of Emain Mhacha, at the site known as Navan Fort, served as the centre of a kingdom of Ulster extending to the Rivers Shannon and Boyne in the west and south. Also associated with that period is an ancient frontier earthwork, Black Pig's Dyke. Following the decline of Ulster in the 4th century, Emain Mhacha lost its importance; and Ard Mhacha (now Armagh, the county town) became the political centre. It gained added importance after St. Patrick made it his metropolitan see in the 5th century. The area was later ravaged by Anglo-Norman and also Danish (841) invaders, but they made no permanent settlements.