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Origin of MacCarthy surname

Bruce A. Johnson


Irish Flag  The information in this article is not meant to be a complete history of the MacCarthys, or of Ireland or Munster.


     The basics to start . . .

   I thought that before I get into a bit of history, I would jump ahead, temporarily, to when the surname was first used.  First, you should know that "mac" in Gaelic means "son of" (it is not just a Scottish thing, but Irish as well).  Before surnames came into use, individuals were known by identifying their father after their name.  If I had lived back then, I would have been known as "Bruce mac Louis", because my father's name is Louis.  It was simple and straightforward, but you had to know who the father was to make any sense of who the individual was.

   It has been said that Brian Boru initiated the practice of using surnames (some debate there), and decreed that a certain name should be imposed on each tribe to denote its origin.  It is probable, at all events, that surnames then became necessary as a more ready and precise means of tribe desgnation than had previously existed.

   Carthach, was a king of Eóghanacht Chaisil who died in 1045 A.D. (pronunciation: 'ch' in Gaelic is like the ch sound in Yiddish (Chanukah) or German (nacht), very guttural and from the back of the throat.)  Carthach's son, Muiredach mac Carthach, was the first of his race to assume the name of "MacCarthaigh", which was anglicized to MacCarthy and its variations later.

   Now, that information by itself doesn't tell you much about the origin of the MacCarthys, and may even raise some questions, so I will now go back to tell you a little bit of history.


     Ireland & Munster

   Early Celtic Ireland was divided into many petty kingdoms, or clans (tuatha), each of which was independent under its elected king.  Around the beginning of the Christian era, the country was divided into five groups of tuatha, known as the Five Fifths (Cuíg Cuígí).  These were Ulster (Ulaidh), Meath (Midhe), Leinster (Laighin), Munster (Mumhain), and Connaught (Connacht).  These were later known as provinces.

   Munster is the southwestern Fifth, kingdom, or province, of Ireland.  It is composed today of the counties of: Clare, Tipperary, Waterford, Limerick, Kerry, and Cork.  The whole of the Kingdom of Munster encompassed some 9469 square miles.  Munster was ruled by the Eóghanachta for much of its existence.

   Munster was not just composed of the Eóghanacht, but also of the Dál gCais.  Much of Munster's history is fraught with conflict between these two septs.  The MacCarthys and their ancestors were Eugenian (another name for those who were of the Eóghanacht), and their chief Dalcassian (another name for those who were of the Dál gCais), rivals were the O'Briens.  The O'Briens are the descendants of (and gain their name from), the famous Brian Boru.

   The Eóghanachta were a race/clan that mythically originated from Heber, eldest son of Spanish king Milesius.  Today, Milesius is regarded at best semi-mythical, if not a complete fabrication of medieval Gaelic monks.


     Eóghan Mór

   Legend says that Eóghan Mór is 46th in descent from Heber.  Eóghan Mór was also known as Eóghan Taídlech or Mug Nuadat.  The latter name was his throne name, and is literally translated as "Slave of Nuadu."  He assumed this name in honour of the dynastic god, Nuadu, over whose cult he probably presided.  Anyway, Eóghan Mór is the farthest back known ancestor of the MacCarthys, and he died about 192 A.D.


     Conall Corc

   Eóghan Mór was the 4th great grandfather of Conall Corc (died in 379 A.D.), who is regarded as the first generally accepted historical king of Munster.  King Conall Corc established Cashel (ancient: Chaisil; in the current county of Tipperary), as the royal seat of Munster.  In the descendants of Conall Corc, the Eóghanacht became six different septs:

   About half of the Kings of Munster were of the Eóghanacht Chaisil.  It must be said, though, that the royal succession was not by primogeniture, which was an unknown concept to the Gaelic.  In general, primogeniture is the succession of the throne from father to son, and if there are no sons, then the next nearest male relative ascends to the throne.  The Gaelic people used the "law" of Tanistry to decide the succession of the throne.  The most simplest explanation of Tanistry is the ascension of throne by the most capable, fit, and wise man of the clan at the time.  This could possibly be a son of the king, but was generally not.  It could be the king's brother, nephew, or even a distant cousin in the clan.


     Donnchad II & Brian Boro

   16 generations down in the Eóghanacht Chaisil from Conall Corc, is Donnchad II, who was also a King of Munster until his death in 963 A.D.  At Donnchad's death, Mathgamain mac Cenneetig of the Dál gCais, and King of Thomond, usurped the throne of Munster.  I'm sure that the Eóghanacht didn't much like that.  In fact, the King of Eóghanacht Raithlind, Máelmauad mac Bran, killed Mathgamain in 976, and assumed the title of King of Munster.  Unfortunately, he himself was killed two years later by Brian Boru (b. ca 941), the half brother of Mathgamain, and Brian assumed the title of King of Munster.

   Under Brian Boru's rule, Munster became a unified and powerful state.  Brian Boru then defeated other Irish rulers and the Norse to become high king of Ireland in 1002.  His Norse and Irish enemies allied against him, but at Clontarf (near Dublin), on Apr. 23, 1014, Brian's army, under the command of his son Murchad, routed the coalition.  Brian was about 73 years old, so did not participate in the battle, but the battle found him anyway.  A small group of Northmen were fleeing the battle, and stumbled across Brian's tent.  They overcame Brian's guards and hacked him to death.

   Even after Brian Boru's death, the Dál gCais reigned supreme in Munster until 1118.

   Meanwhile, the grandson of Donnchad II, Carthach (mentioned at the beginning of this article), reigned as King of Eóghanacht Chaisil, and in 1118, his grandson became the first King of Desmond.


     Treaty of Glanmire, 1118.

   The treaty of Glanmire in 1118 divided the Kingdom of Munster into northern (Tuadh Mumhan = Thomond) and southern (Des Mumhan = Desmond) halves.  The Kingdom of Thomond was ruled by the Dál gCais dynasty of the O'Briens.  The Kingdom of Desmond, which was the greater part, containing some 4,500 square miles in extent, was a Eóghanacht state and was ruled solely the MacCarthys (Eóghanacht Chaisil).  Carthach's grandson, Tadhg I MacCarthy, was the first King of Desmond.

   The Kingdom of Desmond continued until 1596, when King Donal IX MacCarthy Mór died without any surviving legitimate male issue.  His nearest living cousin, Callaghan, 5th Lord of Kerslawny, was his legal heir, and thus became the King of Desmond, but only in name.  Callaghan assumed the title of MacCarthy Mór, and in his descendants were the Princes of Desmond down to the just recently abdicated (Oct 1999), MacCarthy Mór: Terence Francis (Tadhg V) MacCarthy Mór.



  1. McCarthy, Samuel Trant & McCarthy, Terence Francis, The MacCarthys of Munster.  Originally published in 1922 by The Dundalgan Press, Dundalk, Co. Louth, Ireland.  Facsimile edition published in 1997 by Gryfons Publishers & Distributors, Little Rock, AR, USA.
  2. Encyclopædia Britannica (

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