MacCarthy is probably the most common of all the Mac surnames in Irish heritage. The name is most closely associated with counties Cork and Kerry.
Historically, the MacCarthy family were the senior royal dynasty within the Eoghanachta clan group. Between the 6th and 10th centuries, the Eoghanachta ruled as kings of Munster, the richest of all the provinces in Ireland. Their royal seat was the Rock of Cashel, also known as “Cashel of the Kings.”
The MacCarthy surname derives from a real historical figure, Carthy (Carthach). Carthy was both a bishop and a king, combining the authority of church and state in his person. In 1045, he died in an arson attack on his house. His sons and grandsons began to style themselves Mac Carthy—literally meaning “sons of Carthy.”
Other royal dynasties within the Eoghanachta who started adopting fixed surnames include the O’Callaghan, O’Donoghue, O’Donovan, O’Mahony, O’Sullivan, MacGillycuddy, and Moriarty families. As late as the 1600s, these families still recognized MacCarthy as the senior royal family within their wider clan group. Practically speaking, they paid taxes to the MacCarthy chiefs and played a role in inaugurating each new MacCarthy leader.
During inaugurations, for example, the head of the O’Sullivan clan presented a white rod to the MacCarthy chief, symbolizing his role as lawgiver.
Between 1127 and 1134, Cormac MacCarthy, Carthy’s grandson, built a church on the Rock of Cashel and dedicated it to his grandfather. Cormac’s chapel still survives today and stands as one of the earliest and finest ancient churches in Ireland, open to visitors.
Under the native Irish Brehon laws, inheritance rights were equal within four generations. This led to many dynasties within the clan group and gave rise to distinct branches of the MacCarthy family. The most notable branches include:
– MacCarthy Mor, kings of Desmond in Kerry
– MacCarthy Reagh, based in Carbery in West Cork
– MacCarthy Muskerry, near Macroom in County Cork
– MacDonagh MacCarthy of Duhallow, on the border of Kerry and Limerick
The MacCarthys were shrewd politicians. They made war or peace on their own terms and often cemented peace settlements by marrying their sons and daughters to political enemies.
In the 1490s, Donal MacCarthy of Carbery married Lady Eleanor Fitzgerald, daughter of the Earl of Kildare—commonly known as “all but king of Ireland.”
In 1537, Lady Eleanor MacCarthy became a key figure behind the Geraldine League, established after Silken Thomas and his five uncles were executed for rebellion. Eleanor protected the young Geraldine heir, using her alliances with Irish and English families. Under her care, the heir was safely taken to France, where he was raised in exile.
The last MacCarthy king of Desmond was Donal MacCarthy Mor, who controlled Kerry from 1558 until his death in 1596. In 1565, Donal MacCarthy Mor was granted an English title—the Earl of Clancar—as an incentive to abandon Irish laws and customs.
Despite receiving this earldom, MacCarthy Mor remained ambiguous about English settlement in Kerry. In contrast, his daughter Ellen MacCarthy firmly rejected the English settlers, whom she dismissed as “mere English” and “men without pedigrees.”
In 1588, Ellen married her cousin Florence MacCarthy Reagh in a secret midnight ceremony at Muckross Abbey.
Following Donal MacCarthy Mor’s death in 1596, a dispute arose over who should inherit the kingdom of Desmond: Ellen and her husband, or Ellen’s illegitimate half-brother Donal.
Even before MacCarthy Mor’s death, the Tudors had made it clear that MacCarthy influence was waning. By the time the Tudor conquest of Ireland was complete, the power of the MacCarthys in Munster was effectively broken.
However, historical records indicate that descendants from some collateral branches of the MacCarthy family survived the upheaval.
Today, there are over 2.7 million MacCarthy records available on Findmypast, dating from the 1600s onwards.
*This article was originally published in 2014 and was updated in September 2025.*
https://www.irishcentral.com/roots/history/origins-history-surname-maccarthy