Tyrconnel, the district named after the Cinel Connell, where the O'Donnells held sway, comprised the greater part of the modern county of Donegal except the peninsula of Inishowen; and since it lay conterminous with the territory ruled by the O'Neills of Tyrone, who were continually attempting to assert their supremacy over it, the history of the O'Donnells is for the most part a record of tribal warfare with their powerful neighbours, and of their own efforts to make good their claims to the overlordship of northern Connaught.
His brother Domhnall (Donnell) was king of Ailech, a district in Donegal and Derry; the royal palace, the ruined masonry of which is still to be seen, being on the summit of a hill Boo ft.
Following the coast southward, Donegal Bay is divided from Galway Bay by the hammer-like projection of county Mayo and Connemara, the square inlet of Clew Bay intervening.
The union was not perfect; the presbytery of Donegal was for three years in revolt against the synod; and in 1762 a second presbytery of Philadelphia was formed; but the strength of the synod increased rapidly and at the outbreak of the War of Independence it had 11 presbyteries and 132 ministers.
Exceptions, however, are Tory Island and North Aran off the Donegal coast, Achill and Clare off Mayo, the South Arans guarding Galway Bay, the Blasquets and Valencia off the Kerry coast.
The north-west highlands of Donegal and the Ox Mountains, with their axes of folding running north-east and south-west, invite comparison with the great chain of Leinster, but also with the Grampians and the backbone of Scandinavia.
In the north lie Loughs Melvin, close above Donegal Bay, and Gill near Sligo, Lough Gara, draining to the Shannon, and Lough Conn near Ballina (county Mayo), and in the south, the great expanses of Loughs Mask and Corrib, joined by a subterranean channel.
In1730-1732the stricter party in the presbyteries of New Castle and Donegal insisted on full subscription, and in 1736, in a minority synod, interpreted the adopting act according to their own views.