The origins and history of the surname MacCarthy

MacCarthy is probably the most common of all the Mac’s 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 (Cárthach). Carthy was a bishop and king who combined in his person the authority of the church and state. In 1045, he died in an arson attack on his house. His sons and grandsons styled themselves Mac Carthy - literally “sons of.”

Other royal dynasties from the Eoghanachta that began to adopt fixed surnames include O’Callaghan, O’Donoghue, O’Donovan, O’Mahony, O’Sullivan, Macgillycuddy and Moriarty. As late as the 1600s these families still recognised MacCarthy as the senior royal family in their wider clan group: in practical terms they paid him taxes; and they played a role in inaugurating each new MacCarthy ‘chief.’.

The head of the O’Sullivan gave a ‘white-rod’ to MacCarthy during his inauguration, to symbolise his role as ‘law-giver.’

In 1127-34, 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 very many dynasties in the clan group, but it also gave rise 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; and 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 "all but king of Ireland."

In 1537, Lady Eleanor MacCarthy was one of the key figures behind the Geraldine League, set up after Silken Thomas and his five uncles were executed for rebellion. Eleanor MacCarthy kept safe the young Geraldine heir, appealing to friendships and alliances with Irish and English families. Under her protection, he was brought to France where he was raised in safety.

The last MacCarthy king of Desmond was Donal MacCarthy Mor, who controlled Kerry between 1558 and his death in 1596. In 1565 Donal MacCarthy Mor was given an English title, earl of Clancar, as an incentive to set aside Irish laws and customs.

Despite the gift of an earldom, MacCarthy Mor was 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.

In 1596, Donal MacCarthy Mor died, and 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 McCarthy Mor’s (Clancar) death, the Tudors indicated they had decided that McCarthy'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 McCarthy survived.

There are over 2.7 million MacCarthy records on findmypast dating from the 1600s onwards.

* This article was originally published in 2014, it was updated in Sept 2025.