On the death of the previous chief, his brother Fergal Mág Tighearnán in 1383, Cú Connacht took the chieftaincy and resided in the castle of Croaghan of the Cups (Irish- Cruachan O'Cúbhrán), now in the townland of Coolnashinny, besides the modern town of Killeshandra.
The Clann-Muirchertaigh and Tellach-Dunchadha emigrated despite Muinter-Ruairc, towards Fidh-na-finnoige, Sliabh-Corran, and Cenel-Luachain; and O'Ruairc obtained intelligence of this whilst he was in Glenn-Gaibhle; and he brought his bands to the upper part of Cenel-Luachain; and a brave, destructive assault was made by O'Ruairc on these royal divisions, who were routed; and the killing of their flocks continued from Bel-atha-doire-Dubhthaigh to the summit of the Breifnian hills.
The Clan Murtagh and Tellach Dunchada made a forcible migration into the country of the Muinter Ruairc towards Fid O Finnoice, Sliab Corrain and Cenel Luachain.
He conveyed his trains to the upper end of Cenel Luachain and made a fierce and victorious attack on those allied princes and routed them, and kept on slaughtering their cattle from Bel Atha Daire Dubthaig to the top of the Brefne hills.
But as soon as O'Rourke, who was at that time in Glenn-Gaibhle, received notice of this, he took his scouts with him to the upper part of Kinel-Luachain, where he made an attack on them, and forced them to fly before him, killing both cattle and people on their route from Beal-atha Doire-Dubhain to the summit of the Breifnian hills.
Magnus o'Roirck remayned prisoner with o'Relly in the Island of Loghoghter, from whence he went to the castle of Loghskwyre, where being betrayed to the sonns of Murtagh, they killed him as hee was leaving the Coytt.
O'Roirck hearing thereof being at ffye Gaiule, brought his preyes and people with him to a place called Barre and from thence he assaulted the said parties his adversaries, ouerthrew them, killed many of their people and Cattle, and held on his course of killing them from Belagh Derg to the top of the place called Tullagh Brefnagh; On 14 April 1405 his first cousin once removed died- Áine, daughter of a previous chief Brian Mág Tighearnán.
The Annals of Ulster for 1412 state- Cu-Connacht Mag Tignernain, chief of Tellach Dunchadha, was killed by the Fir-Manach in his own house on Cruachan on a night incursion.
And they inflicted a massacre of women and men and children there and burned the town of Mag Tigernain on that expedition and came to their houses safe from that excursion.
The Annals of the Four Masters for 1412 state- Cuconnaught Mac Tiernan, Chief of Teallach Dunchadha, was killed by the people of Fermanagh, in a nocturnal assault, in his own house at Cruachan Mhic-Tighearnain.