The Dalcassians of Ireland
Chiefs of Muintirfernain County Clare
Chiefs of Owneybeg County Limerick
According to the Irish Families' Historical Society, Inc of New Jersey......
The Heffernans are descended from Milesius, King of Galacia in Spain.
Through the line of Heber (Eber), his son. Heber became the first
Milesian king of Ireland in 1699 bc, ruling jointly with his brother Heremon
(Eremon). Heber died a year later and Eremon ruled for another 14
The Dalcassian Clan was known for its fierceness in battle and was a major force with Brian Boru in wiping out the Vikings. (Which very nearly wiped out the Dalcassians.)
The Heffernans are more directly descended from Cormac Cas, the grandson of Owen the Great who won half of Ireland from Conn of the Hundred Battles.
The Clan of Heffernan originally inhabited a territory near Corofin, County Clare, called Muintirfernain after them. They established themselves in eastern County Limerick on the Tipperary border and were Chiefs there of Owneybeg, where after a period of time they were displaced by the Ryans.
The old manuscripts, such as the Book of Rights, describe the OHeffernans as one of the four tribes of Owney, the others being MacKeogh, OLoingsigh (Lynch) and OCalahan. The two most distinguished memebers of the Heffernans were Aeneas OHeffernan who was the Bishop Of Emily, 1543-1553, and William Dall OHeffernan (1715-1802), Gaelic poet.
The original text of this quote is here.