According to historian C. Thomas Cairney, the O'Mearas were one of the chiefly families of the Dal gCais or Dalcassians who were a tribe of the Erainn who were the second wave of Celts to settle in Ireland between about 500 and 100 BC.
[1] The Ó Meadhra clan were a sept of the Dal gCais, and the name is most common in the dynasty's homeland of north-east Thomond (presently County Tipperary and the adjoining parts of County Clare).
[2] Members of the family were physicians and poets to the Earl of Ormond.
The last Gaelic-era Chief of the Name was Domhnall Ó Meadhra.
[citation needed] Ó Meadhra was Anglicized as O'Meara and O'Mara, both of which may not necessarily have an "O'" prefix.