Recorded in a number of spellings including MacKernan, McKernan, McKearnen, McKiernan, McTiernan, Kiernan and Kernon, this is an Irish surname. It originates from the pre 10th century Olde Gaelic name 'Mac Thighearnain' meaning 'The son of the Lord', a translation which no doubt helped its popularity considerably. The clan or sept originally belonged to Breffny, an ancient province comprising the modern counties of Cavan and Leitrim. Their chiefs were known as the Lords of Teallach Donnchadha, the modern Tullyhunco, in County Cavan, and frequent reference was made to their exploits in ancient Irish Annals from 1250 to 1550. The name is still chiefly found in the Cavan-Leitrim area. When the prefix "mac" is retained McTiernan is now the most popular spelling. Another branch of the family held territory with the O'Conors in East Connacht, whilst a third sept settled in County Fermanagh. The first recorded spelling of the family name is shown to be that of Teag MacKiernan, and dated 1250, in "The Annals of the Four Masters", during the reign of the Norman Conquerors of Ireland, 1224 - 1260. Surnames became necessary when governments introduced personal taxation. In England this was sometimes known as the Poll Tax. Throughout the centuries, surnames in every country have continued to "develop" often leading to astonishing variants of the original spelling.