[1] On the death of the previous chief, Tadhg took the chieftaincy and resided in the castle of Croaghan of the Cups (Irish- Cruachan O'Cúbhrán, now the townland of Croaghan), now in the townland of Coolnashinny, besides the modern town of Killeshandra.
In 1470 the O’Rourkes and their allies the O’Donnells, tried to inaugurate Domhnall O’Rourke, who was the O'Rourke chief from 1468 to 1476, in the McKiernan castle of Croaghan but the McKiernans successfully resisted the invasion at Ballyconnell town with the help of the O’Reillys and the English.
O'Reilly, the English, and the people of Teallach-Dunchadha, the Mac Kernans, opposed them at Beal-atha-Chonaill, where Edmond, the son of Hugh O'Reilly, and the son of the Bishop O'Gallagher, were slain, and many men and horses wounded.
The Annals of Connacht for 1472 state- The posterity of Mathgamain O Raigillig utterly routed the Tellach Dunchada and their allies of Brefne and Muinter Eolais, killing two sons of Ruaidri O Raigillig and many others gentle and simple.
The Annals of Ulster for 1474 state- Mag Tighernain of Teallach-Dunchadha, namely, Tadhg, died the same year.