Fergal mac Gíolla Íosa Óg Mág Tighearnán (anglicised Fergal McKiernan) was head of the lineage of McKiernan Clan of Tullyhunco, County Cavan from 1512 until his death in 1523.
[2] Fergal's brother succeeded him as chief of the clan on his death.
On the death of the previous Ceann fine ('head of the lineage'), William Mág Tighearnán in 1512, Fergal took over and resided in the castle of Cruachan Ua Cúbhrán, now in the townland of Coolnashinny, besides the modern town of Killeshandra.
The Annals of Connacht for the year 1523 state- Mag Tigernain, Fergal son of Gilla Isa Oc son of Gilla Isa son of Brian, chieftain of Tullyhuncoe, a charitable humane man, died at his own residence and his brother succeeded him.
The Annals of Loch Cé for the year 1523 state- Mac Tighernain, i.e. Ferghal, son of Gilla-Isa Og, son of Gilla-Isa, son of Brian, dux of Tellach-Dunchadha, a charitable, humane man, died in his own town; and his brother assumed his place after him.