Dál gCais -- (Dalcassion) the race of Cas, the sixth in descent from Cormac Cas, son of Oilioll Olum, King of Munster in the 3rd century. Through this line they are connected to Cashel and the other great families of the province of Munster. This great clan of Thomond (North Munster), holds several distinguished families including the Chief family of the name, the O'Briens. The clan of the noted high king, Brian Boru. The Dalcassians: According to Connellan, the Chief families of this sept were--

  • Lysacht
  • MacArthur
  • MacBruodin
  • MacClancy
  • MacConry
  • MacCurtin
  • MacDonnell
  • MacEniry
  • MacGrath
  • MacMahon
  • MacNamara--
    • Clann Chuileainn - the race of Cuilean, another branch of the Dál gCais. One of several clan names which apply to the MacNamaras and their co-relatives in Thomand.
    • Uí Caisin - descendants of Caisin, son of Cas, the name of a branch of the Dál gCais of which MacNamara was Chief.
  • O'Ahern
    • Uí Bloid - descendants of Blod, son of Cas, a branch of the Dál gCais. This clan includes the O'Kennedy, O'Shanahan, O'Durack and O'Ahern families of eastern Co. Clare. The name is still preserved in the place name of the deanery of Omulled.
    • Uí Cearnaigh - descendants of Cearnach, the branch of the Dál gCais of which the Ahernes were Chiefs.
  • O'Brien
    • Bernard
    • Bryan
    • Bryant
    • MacConsidine
    • O'Crotty
    • Mahony
    • Lysaght
    • MacMahon
    • Padden
    • MacFadden
    • Plunkett
  • O'Brody
  • O'Casey
  • O'Cashin
  • O'Considine
  • O'Connor
    • Corca Modhruadh - the race of Modruadh, son of Fergus MacRoigh. This is the name of a 'great clan' in the north-west of Co. Clare. Their territory was co-extensive with the Diocese of Kilfenora. The Chief families of this clan were the O'Loughlins and the O'Connors. They were not a Dalcassion clan.
  • O'Davoran
  • O'Dea
  • O'Duhig
  • O'Grady
  • O'Hanraghan
  • O'Hartigan
  • O'Hea
  • O'Healy (modernized Haley and Hayley)
  • O'Heap,
  • O'Heffernan
  • O'Hehir
    • Uí Cormaic - descendants of Cormac, the clan name of the O'Hehirs in Thomond.
  • O'Hickey
  • O'Hogan
  • O'Hurly (modernized Harley)
  • O'Kearney
  • O'Kennedy
    • Uí Bloid - descendants of Blod, son of Cas, a branch of the Dál gCais. This clan includes the O'Kennedy, O'Shanahan, O'Durack and O'Ahern families of eastern Co. Clare. The name is still preserved in the place name of the deanery of Omulled.
  • O'Liddy
  • O'Lonergan
  • O'Loughlin
    • Corca Modhruadh - the race of Modruadh, son of Fergus MacRoigh. This is the name of a 'great clan' in the north-west of Co. Clare. Their territory was co-extensive with the Diocese of Kilfenora. The Chief families of this clan were the O'Loughlins and the O'Connors. They were not a Dalcassion clan.
  • O'Meara
  • O'Molony
  • O'Noonan (or O'Nunan)
  • O'Quinn
  • O'Shanahan (or O'Shannon)
    • Uí Ronghaile - descendants of Ronghal, a branch of the Dál gCais of which the O'Shanahans were Chiefs.
    • Ui Bloid - descendants of Blod, son of Cas, a branch of the Dál gCais. This clan includes the O'Kennedy, O'Shanahan, O'Durack and O'Ahern families of eastern Co. Clare. The name is still preserved in the place name of the deanery of Omulled.
  • O'Sheehan
  • O'Slattery
  • O'Spillane
  • O'Twomey
  • etc
The following were also of the Dalcassian race: the families of MacCoghlan, Chiefs in the King's County;
  • O'Finnelan (or O'Fenelon)
  • O'Skully, Chiefs in Teffia, or Westmeath
Cenél Cuallachta - the race of Cuallachta or Collachtach; a branch of the Dál gCais or Dalcassions. These families are descended from Aonghus Ceannathrach, son of Cas, and centered in the barony of Inchiquin, Co. Clare. O'gRiobta was the Chief family of this tribe.
Muintear Ifearnain - The family of Ifearnan, a branch of the Dál gCais. This was the clan name of the O'Quinns of Thomand who descend from Ifearnan, son of Corc, the 15th in descent from Cormac Cas, the ancestor of the Dál gCas or Dalcassions.


Uí Toirdealbhaigh - descendants of Toirdealbach (Father of St. Flannan), King of Thomand. The clan name of the O'Briens and their co-relatives in the east of Co. Clare.

Corca Bhaiscinn - the race of Cairbre Baschaoin, centered in the south-west of Co. Clare. [Not Dalcassian].

'Irish Pedigrees' by O'Hart, Vol I. 'The Surnames of Ireland' by Edward MacLysaght'. The Book of Irish Families Great & Sl' by Michael C. O'Laughlin. 'Irish Families' by Edward MacLysaght 'More Irish Families' by Edward MacLysaght.