Mooney is a family name, which is probably predominantly derived from the Irish Ó Maonaigh. It can also be spelled Moony, Moonie, Mainey, Mauney, Meaney and Meeney depending on the dialectic pronunciation that was Anglicised.
The origin of the different Moony or Mooney families is lost in antiquity. The name is derived from maoin a Gaelic word meaning wealth or treasure of treasure, hence when O'Maonaigh was anglicised to Mooney it meant the descendant of the wealthy one.
According to Irish lore, the Mooney family comes from one of the largest and most noble Irish lines. They are said to be descendants of the ancient Irish King Heremon, who, along with his brother Herber, conquered Ireland. Heremon slew his brother shortly after their invasion, took the throne for himself, and fathered a line of kings of Ireland that include Malachi II, and King Niall of the Nine Hostages.
Baptismal records, parish records, ancient land grants, the Annals of the Four Masters, and books by O'Hart, McLysaght, and O'Brien were all used in researching the history of the Mooney family name. These varied and often ancient records indicate that distant septs of the name arose in several places throughout Ireland. The most known and most numerous sept came from the county of Offaly. The members of this sept were from Chieftain Monach, son of Ailill Mor, Lord of Ulster, who was descended from the Kings of Connacht. These family members gave their name to town lands called Ballymooney both in that county and in the neighbouring county of Leix.