Donahue is the Americanized version of Irish surname Donohoe, which, in turn, is an Anglicized version of the ancient Irish name "Donnchadh" (sometimes "Donncha").
There are eight known O'Donoghue tribal areas in Ireland; in Munster the areas of Tipperary, Cork and Kerry, then there are Kilkenny, Wicklow, Dublin and Meath in Leinster and in Connaught there are Galway, Mayo, Sligo and Cavan.
Considerable migration took place over the centuries and family groups took root in many other counties (e.g. Clare, Limerick, Waterford, Roscommon, and others), which would today be recognised as their areas of origin.
The Donohoes of the ancient Kingdom of Breifne, centered in modern-day County Cavan, are genetically linked to 4th-century Irish warlord Niall of the Nine Hostages.
Of 2,800 families reporting variations of the name at the time of Griffith's Valuation (1847–1864), 2,483, or 88%, were listed as Donohoe.