From the plain of Tochuir at Carndonagh, St.Patrick came into Dolu Ocheni- also known as the Valley of Faughan- and established 7 churches as named: Domnach Dola, Domnach Senliss, Domnach Dari, Domnach Senchue, Domnach Min-cluaine, Domnach Cati and Both Domnach. Some of these monastic foundations include Clooney and Gransha.
During this period Enagh was founded by St. Canice, as well as the establishment of St Canice's Church in St Columb's Park.
From Inishowen where the Cineal Eoghain had originally settled themselves, there spread out many branches of the family seeking lands to establish themselves in. One of the strongest of these was the Clann Chonchobair, who after hard fighting won for themselves Magh Iotha,that fertile plain south of Derry known today as the Lagan.
After a time, the old problem arose once more, too many people, too little land and therefore the tribe were pushing out again. Thus, it came about that the Ul Caireallain the family of Caireallain, grandson of Diarmuid, son of Chonchobhar, found themselves in what today is our parish, and thus it was that the name Glendermott, or more accurately, Clandermott,. The history of the parish for the next few centuries is mainly the story of the Clann Diarmuda, but the account is far from complete, the only evidence surviving is the entries in the Annals.
The battle of Belad took place in 1076. The precise location of the battle is suggested to be in the Altnagelvin-Lisnagelvin district.
There was further violent episode in the year 1200 when the O’Donnells attacked the Clan Dermott by sea. Their ships, thirteen in number, sailed up the Foyle, and landed a force at Port-Rois, our Rosses Bay.
The Clan Dermott immediately engaged them, but were completely routed, and the O’Donnell’s pursuing them up closely inflicted heavy slaughter. Six years later, the Tirconnell tribe invaded Glendermott again, and once more were victorious, in this instance carrying off a great prey of cattle.