MacCarthy is probably the most common of all the Macs in Irish surnames. The name is most closely associated with counties Cork and Kerry.
Historically, the MacCarthy were the senior royal dynasty in the Eoghanachta clan group. Between the 6th and 10th centuries, the Eoghanachta were kings of Munster, the richest of all the provinces in Ireland. Their base was the Rock of Cashel, also known as “Cashel of the Kings.”
The MacCarthy family name derives from a real historical figure, Carthy (Carthach). Carthy was a bishop and king who combined in his person the authority of both the church and state. In 1045, he died in an arson attack on his house. His sons and grandsons styled themselves Mac Carthy, literally meaning “sons of Carthy.”
Other royal dynasties from the Eoghanachta began to adopt fixed surnames during this period, including O’Callaghan, O’Donoghue, O’Donovan, O’Mahony, O’Sullivan, MacGillycuddy, and Moriarty. As late as the 1600s, these families still recognized MacCarthy as the senior royal family in their wider clan group. In practical terms, they paid him taxes and played a role in inaugurating each new MacCarthy chief. For example, the head of the O’Sullivan gave a white rod to MacCarthy during his inauguration to symbolize his role as law-giver.
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 survives to the present day and is one of the earliest and finest ancient churches in Ireland open to visitors.
Under the native Irish (Brehon) laws, there was equal right to inherit within four generations. This not only gave rise to many dynasties within the clan group but also led to distinct branches in the MacCarthy family. The most important of these were:
– The MacCarthy Mór kings of Desmond in Kerry
– MacCarthy Reagh based in Carbery in West Cork
– MacCarthy Muskerry, near Macroom in Co. Cork
– MacDonagh MacCarthy of Duhallow, on the border of Kerry and Limerick
The MacCarthy were clever politicians. They made war or peace on their own terms and often concluded peace settlements by marrying their sons and daughters to their political enemies.
In the 1490s, Donal MacCarthy of Carbery married Lady Eleanor Fitzgerald, daughter of the Earl of Kildare, who was considered “all but king of Ireland.” In 1537, Lady Eleanor MacCarthy was one of the key figures behind the Geraldine League, which was established after Silken Thomas and his five uncles were executed for rebellion. Eleanor MacCarthy safeguarded the young Geraldine heir, appealing to friendships and alliances with both Irish and English families. Under her protection, he was brought to France where he was raised safely.
The last MacCarthy king of Desmond was Donal MacCarthy Mór, who controlled Kerry between 1558 and his death in 1596. In 1565, Donal MacCarthy Mór was given an English title, Earl of Clancar, as an incentive to abandon Irish laws and customs. Despite this gift, MacCarthy Mór remained ambiguous about English settlement in Kerry.
In contrast, his daughter Ellen MacCarthy was quite certain about her own prejudices and refused to marry any of the English settlers in Ireland, whom she dismissed as “mere English” and “men without pedigrees.” In 1588, Ellen MacCarthy married her cousin Florence MacCarthy Reagh in a secret midnight ceremony in Muckross Abbey.
When Donal MacCarthy Mór died in 1596, there was a dispute over who should inherit the kingdom of Desmond: Ellen and her husband, or Ellen’s illegitimate half-brother Donal. Even before MacCarthy Mór’s (Clancar) death, the Tudors had indicated they had decided that the MacCarthy’s influence was over.
By the time the Tudor Conquest was complete, the power of the MacCarthys was broken in Munster. However, historic records show that descendants from some of the collateral branches of the MacCarthy survived. There are over 2.7 million MacCarthy records 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
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