Mac Mathghamhna

McMahon or MacMahon (older Irish orthography: Mac Mathghamhna reformed Irish orthography: Mac Mathúna) is an Irish surname. The surname arose separately in two areas: in west County Clare and in County Monaghan. The County Monaghan (Airgíalla) MacMahons are not related to the County Clare (Thomond) MacMahons.

The Thomond MacMahons were part of the great tribal grouping, the Dál gCais, and claimed descent from Mahon O'Brien, grandson of Brian Ború. The last chief of the name was killed at the battle of Kinsale in 1602, and the chiefly line became extinct.

After the defeats of the native Irish in 17th century, many of the Clare MacMahons emigrated to serve in the Irish Brigade of the French Army. John Baptiste MacMahon, descended from the MacMahon female line, took on the surname of MacMahon and was the son of one of the original members of the Irish Brigade. He was made Marquis d’Eguilly by Louis XV. He had wanted to marry into a noble family but had to prove he was a noble. The name was changed through the female line because France recognised the line through a female, unlike Ireland to this day.

His grandson, Patrice de MacMahon (1808–1893), was created Duke of Magenta, became a field marshal and later the French president. The MacMahon family are still prominent in France; the family home is the Château de Sully outside Bordeaux.

The Oriel (Anglicisation of Airgíalla) MacMahons were based in the barony of Truagh in the north of County Monaghan and ruled the kingdom of Oriel between the thirteenth and the sixteenth centuries. Their last chief, Hugh Oge MacMahon, who had become a lieutenant-colonel in the Spanish army, was beheaded by the English in 1641. A separate McMahon family in County Fermanagh is descended from Mahon Maguire, a grandson of Donn Carrach Maguire. Today, although widespread throughout Ireland, MacMahon remains most common in the two ancestral homelands of Counties Clare and Monaghan.

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