McKinley is a Scottish and Irish surname historically associated with northwestern Ireland's County Donegal, and the over-kingdom of Ulaid in northeastern Ireland and the Scottish Highlands. The McKinley are of the ancient Ulaid race and are a branch of its "Red Branch" MacDunleavy (dynasty) royal house of the Dal Fiatach which dominated the kingship of the over-kingdom of Ulaid (original Gaelic language Mac Duinnshléibhe). Entomology for the origins of the surname proposes that the Anglicized surname McKinley, like the surname MacNulty (Gaelic Mac an Ultaigh, trans. "son of the ultonian, ulidian or ulsterman", arose originally from a Gaelic nickname given the deposed MacDunleavy dynasty royals while exiled in Tirconnell and elsewhere. Being, also, one of Ireland's ancient hereditary medical families, the MacDunleavy (variant English spelling MacDonlevy) were in Tirconnell accorded the high Gaelic status of "ollahm leighis" or the official physicians to the O'Donnell clan in County Donegal and practiced as physicians while exiled in Argyll, Scotland. The nickname was Mac an Leigh. Per this scenario the Gaelic language patronymic forming prefix "Mac" (meaning "descended of") is joined to the Gaelic language "Léigh" meaning leech, but denoting a physician. Leeching (medical) having been for millennia, in Gaelic Ireland and elsewhere, a commonly employed medical practice.
Notable people surnamed McKinley include: