There is no exact known date for the founding of the parish. In the sixteenth century, Mahoonagh was divided up into three parts called Trean Tawnaghe, Treanmeane and Treanfaltaghe.
Cormac MacCarthaigh became the King of Munster in 1123 when his brother
Tadhg died. According to Mainchín Seoighe, Cormac was known as
Cormac Muighe Thamhnach because he had his residence in Mahoonagh. Cormac
was a violent leader and led an expedition against the O'Connor's of
Connacht. However, he was displaced as King in 1127 and was killed in
1138 in his house in Maigh Thamhnach by the O'Briens. Previously, it
was recorded that Cellachan, the King of Cashel was killed at Mahoonagh