The Conmhaicne (Old Irish [ˈkˠʰɔnˠβ̃ɑkʲːnʲɛ]) were a people of early Ireland, perhaps related to the Laigin, who dispersed to various parts of Ireland. They settled in Connacht and Longford, giving their name to several Conmaicne territories. T. F. O'Rahilly's assertion the Conmaicne were non-Goidelic is not widely accepted.
Their name originates from a mythical ancestor known as Conmac(c) (Old Irish [ˈkˠʰɔnˠβ̃ɑkˠː]), meaning "hound-son" (con, prefix form of n-stem cú hound; mac, son). Conmac(c) descended from Fergus mac Róich and Queen Medb of Connacht. However, Walsh stated "Conmac son of Fergus is a genealogical fiction". The word Conmaicne means "progeny of Conmac" (-ne, a progeny). The name in Old Irish spelling contains m (without a following h) and c (or more etymologically, cc), thus Conmac(c) and Conmaic(c)ne, but in Modern Irish spelling contains mh (with unetymological h as a sign of lenition) and single c, thus Conmhac and Conmhaicne).
Branches of the Conmaicne dispersed to various places.
The Diocese of Ardagh was established in 1111 as the see for east Connacht. Fourteen years later, at the Synod of Kells-Mellifont, its area was reduced to the territory of the Conmaicne Rein and Conmaicne Angalie, south county Leitrim and all county Longford. The diocese was commonly called "the Diocese of the Conmaicne".
Known Septs of the Conmhaicne Rein in south County Leitrim were:
John O'Donovan wrote:
The chief families of the Conmacians were the O'Fearralls, princes and lords of Annaly, or Longford; the Mac Rannalls, a name anglicised to Reynolds, who were Lords of Conmaincee of Moy-Rein and Muintir-Eolais, in Leitrim; the Mac Keoghes, who were chiefs in Galway, and also in Lenister; the MacShanleys; O'Rodaghans; MacDorchys; O'Mulveys; O'Morans, and O'Mannings, chiefs and clans in various parts of Longford, Leitrim, and Roscommon.
Notables descended from the Conmhaicne include Cruimthear Mac Carthaigh, St. Jarlath of Tuam and some abbots of Clonmacnoise.