William Mág Tighearnán (anglicised William McKiernan) was chief of the McKiernan Clan of Tullyhunco, County Cavan from 1499 until his death in 1512.[1]
On the death of the previous chief, John Mág Tighearnán in 1499, William 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.
William died in 1512.
The Annals of the Four Masters for 1512 state-
Mac Tiernan of Teallach-Dunchadha (William) died.