Ulsterancient Ulaidone of the ancient provinces of Ireland, and subsequently the northernmost of Ireland’s four traditional provinces (the others being Leinster, Munster, and Connaught [Connacht]). Because of the Ulster cycle of Irish literature, which recounts the exploits of Cú Chulainn and many other Ulster heroes, Ulster has a place of great prominence in Irish literature. The name Ulster is now commonly applied to used by many to refer to Northern Ireland.

Ancient Ulster extended from the northern and northeastern coasts of Ireland south to what is now County Louth and west to what is now County Donegal. About the beginning of the Christian era, when the ancient provinces of Ireland were first taking permanent shape, Ulster had its capital at Emain Macha, near Armagh. Attacks from the midland kingdom of Meath (Midhe, or Mide) led to Ulster’s disintegration in the 4th and 5th centuries. The province subsequently split into the three kingdoms of Oriel, or Airgialla (in central Ulster), Aileach (in western Ulster), and the smaller kingdom of Ulaid (in eastern Ulster).

During the Anglo-Norman invasion of Ireland in the late 12th century, one of the baronial adventurers, John de Courci, captured eastern Ulster and ruled that small kingdom until dispossessed in 1205 by King John, who created Hugh de Lacy (d. 1242) earl of Ulster. From 1263 to 1333 the earldom was held by the Anglo-Norman family of de Burgh, passing then to an heiress who married Lionel, duke of Clarence, a son of King Edward III, and ultimately to the crown.

In the 16th century Ulster was administratively divided into nine shires (counties), of which those in the republic of Ireland still exist. Meanwhile, the O’Neills (of County Tyrone) and the O’Donnells (of County Tyrconnell) had become virtually supreme in much of Ulster. These two Roman Catholic clans were involved in a serious rebellion against Queen Elizabeth I from 1594 to 1601, caused in part by attempts to impose the English Reformation on the Irish. The failure of negotiations with James I led to the flight of the northern earls of Tyrone, Tyrconnell, and many others in 1607. Soon afterward thousands of settlers, mainly Lowland Scots Presbyterians, were introduced into Ulster, and particularly into its eastern portions, which became predominantly Protestant as a result. Their descendants prospered, and their refusal to join the rest of Ireland in accepting Home Rule led to the establishment of the state of Northern Ireland in 1920, consisting of the six Ulster counties of Antrim, Down, Armagh, Londonderry, Tyrone, and Fermanagh (replaced in the early 1970s by 26 local districts). The three Ulster counties of Monaghan, Cavan, and Donegal were included in the Republic of Ireland. Area of Irish portion of Ulster, 3,123 square miles (8,088 square km). Pop. (2002) Irish portion of Ulster, 246,714; (2006) Irish portion of Ulster, 267,264.