The Irish name McCarty is associated with south Munster or Desmond. The third century King of Munster, Oilioll Olum, had two sons Eoghan and Cormac Cas. At his death North Munster (Thomond) was inherited by the latter (whence the Dalcassians), and South Munster (Desmond) by Eoghan. The families which descended from this Eoghan were known, before the introduction of surnames, as the Eoghanacht, and the surname MacCarty (in Irish Mac Cárthaigh) is derived from Cárthach, lord of the Eoghanacht, who, the Four Masters tell us, met his death in a house deliberately set on fire by one of the Lonergans in 1045. Carthach was King of Cashel circa 1040, at a time when Donncha, son of Brian Boru, was King of Munster.