The Uí Fiachrach were a dynasty who originated in, and who's descendants later ruled, the coicead or fifth of Connacht at different times from the mid-first millenium onwards. They claimed descent from Fiachrae , an older half-brother of Niall Noigiallach or Niall of the Nine Hostages. Fiachrae and his two full brothers, Brion and Ailill, were the collective ancestors of The Connachta dynasty that eventually became the new name of the province.

The other two dynastys within the Connachta were the Ui Briuin - descendants of Brion - and the Tir nAilello - descendants of Ailill. The latter sank into obscurity at an early stage but both the Ui Fiachrach and Ui Briuin and their many sub-septs featured prominently in the history of Connacht for one thousand years. In the 12th centuary, an Ui Briuin descendant, Ruaidri mac Tairrdelbach Ua Conchobair, became High King of Ireland.

The Uí Fiachrach separated into two distinct branches, situated widely apart from each other. The Ui Fiachrach Aidhne settled in the kingdom of Aidhne and established themselves as its new ruling dynasty. The Ui Fiachrach Muaidhe were based along the River Moy in what is now part of Co. Mayo and Co. Sligo . It appears that they once constituted a single overkingdom, and ruled or took tribute from the older tribes and nations situated between Aidhne and Muaide , but lost their grip on power by the early 8th centuary leaving them confined to their own strict territory.

Ui Fiachrach Aidhne was bounded on the north and east by the powerful independent kingdom of Hy-Many or Ui Maine ; to the west by Lough Lurgan (Galway Bay) and the Corco Mo Druad (Corcomroe ); and to the south by In Deis Tuisceairt (later the Dal gCais , later still the O'Brian 's of Thomond. The territorial gains made by the Ui Fiachrach were lost and the kingdom seems to have reverted to something of its original size for its subsequent history.

Up to the mid-12th centuary its lords were the family of O'Cahill , who were overturned and exiled by their kinsmen, the Clan O'Shaughnessy. This family remained rulers of the territory until the land confiscations of the late 1690's and early 1700's; the senior line died out in 1784.

Ui Fiachrach Muaidhe covered all of what is now Co. Sligo and much of north and central Co. Maho . In 982 Aedh ua Dubhda (Aedh grandson of Dubhda), King of Ui Fiachrach Muaidhe, died "an untroubled death." He was the first of his dynasty to use the surname O Dubhda (ang; O'Dowd, Dowd). Brian, Melaghlin Carragh, Connor Oge, and Murtogh mac Connor O Dubhda fought at the Second Battle of Athenry in 1316, only Brian surviving. However by the 14th centuary their power was much reduced, as was their territory which now almost entirely consisted of the barony of Tireragh . For this reason they were no longer referred to as Kings, but as Taoiseach (Chieftain) of Ui Fiachrach Muaidhe.

Here the family became sponsors of the Clan Mac Fhir Bhisigh, a family of herditary historians and judges. Because of this, the O Dubha is singular in having his inauguration ceremony preserved in an old book, the Great Book of Lecan . Written between 1397 and 1418 at Enniscrone in Tireagh, it was commissoned by Tadhg Riabhach O Dubha.

A later Tadgh O Dubhda, Tadhg Buí, became Taoiseach in 1595. In 1601 he led the men of Ui Fiachrach south to Kinsale, never to return. A tradition states that "he survived the battle and settled in Co. Kerry, where his family later became known as Doody." The last true O Dubha of Ui Fiachrach was Dathi Og, patron and lord of Dubhaltach MacFhirbhisigh. Bearers of the name are still found scattered through Sligo, Mayo and Galway.

Genealogy of the early Ui Fiachrach

Bold print indicates Kings of Connacht

           Eochaid Mugmedon
          =Mongfind       + Cairenn
             |                  |
    _________|_________         |
    |        |        |         |
    |        |        |         |
    Brion  Fiachrae  Ailill     Niall, died c.450. 
             |                   (Ui Néill)
    _________|________________________
    |                 |             | 
    |                 |             |
    Amalgaid          Nath Í       Macc Ercae
                      |
   ___________________|_____________________
   |           |                           |
   |           |                           | 
   Fiachnae    Ailill Molt, d.482.         Echu
   |                                       |
   |                                       |
  (Ui Fiachrach Muaidhe)           (Ui Fiachrach Aidhne)

Ui Fiachrach Muaidhe

   Fiachnae
   |
   |
   Elgach
   |
   |
   Maeldubh
   |
   |
   Tipraite
   |
   |
   Dunchad Muirisci
   |
   |_______________________________________________
   |                              |                |  
   |                              |                |
   Indrechtach, d.707.            mac Dunchad      Ailill
   |                              |                | 
   |                              |                |
   Ailill Medraige, d.764.        Tipraite, d.719  Cathal
   |                              |
   |                              |
   Cathal, d.816.                 Donn Cothaid, d.787.      

Ui Fiachrach Aidhne

   Echu
   |
   |
   Eogan
   |
   |
   Conall
   |
   |____________
   |          |
   |          |  
   Gabran     Goibnenn, fl. 538.
   |
   |
   Cobthach
   |
   |
   Colman, d. 622.
   |
   |_____________________________________
   |                                   |
   |                                   |
   Laidgnen/Loingsech, d. 655.         Guaire Aidne, d. 663.
                                       |
   ____________________________________|
   |                                   |        
   |                                   |      
   Muirchertach Nar, d.668.            Artgal  
                                       |  
                                       |                                          
                                       Fergal Aidne, d. 696. 

Sources

• "Irish Kings and High Kings", Francis John Byrne, Dublin, 1973.
• "Leabhar Mor Genealach", Dubhaltach Mac Fhir Bhisigh (ed. Nollaig O Muraile, 2004).
• http://www.fatherdowd.net/dowdstuff/dowdclan.htm