Until the mid-thirteenth century the leading family of the Cineal Eoghain was MacLoughlin (Mac Lochlainn) of lnishowen; in 1241 they lost a decisive battle to their kinsmen the O’Neills, and afterwards they declined in power, though a branch became established in County Leitrim under the O’Rourkes.

The great O’Neills (O Neill) themselves descend from Niall Glundubh, High-King of Ireland, who fell fighting against the Vikings near Dublin in 919. His grandson Domhnall, who flourished about 943, was the first to bear the dynastic name of O’Neill. They were the chief family of the Cineal Eoghain from 1241, and as overlords of Tir Eoghain (which included the modern counties of Tyrone, Derry and those northeastern parts of Donegal), and kings of Ulster they make a very distinguished group in history from the eleventh to the seventeenth century. Such O’Neill magnates as Conn, Shane the Proud, Sir Phelim and Owen Roe are all outstanding figures. A powerful branch of the family settled in Antrim and Down in the fourteenth century, where they were known as Clann Aodha Bhuidhe, or the O’Neills of Claneboy. Other branches of the O’Neills include the O’Branigans (O Branagain) of Derry, who provided eranachs (hereditary abbots) to the churches of Derry in County Derry and Derryvullan in County Fermanagh; the O’Rahillys (O Raithile) of Kerry, a literary family that settled early in County Kerry near Killarney, and the MacMartins (Mac Mairtin) of County Tyrone.

The O’Cahans (O Cathain) were a great family in County Derry, sub-kings of the Cineal Eoghain, whose heads were privileged to be one of the hereditary inaugurators of the O’Neill. They rose to great power during the twelfth century, and were lords of Keenaght, being possessed of the greater part of what is now County Derry until their lands were confiscated by the English in the Ulster Plantation of the sixteenth century. A branch settled in Thomond (northeast Munster). There is a sixteenth-century O’Cahan knight’s effigy at Dungiven in County Derry. The Monros (Mac an Rothaich), derive their name from a place at the foot of the River Roe in Derry, and according to the Clan Donald tradition, they came into Scotland in the train of a daughter of the O’Cahan that became a MacDonald princess. They possessed the vast district of Foulis on the Cromarty Firth in Ross, and also lands in Strathoykell.

The Roses (Rois, Ros) take their name from the district of Ross in northern Scotland, and are connected with the O’Cahans by the Clan Donald seanachies (historians). Hugh Rose of Geddes witnessed the foundation charter of Beauly Priory by the Bissets. They acquired their principal holdings, the Barony of Kilvarnock in Nairnshire, by marriage with an heiress. They may have acquired their O’Cahan connection win the same way, by marriage, and may originally have been of Norman origin.