Magennis, also spelled Maguiness, McGuinness or Guinness, is an Irish surname, derived from Irish: Mac (or Mag) Aonghusa or the Sons of Angus, sometimes also spelt as Maginnis. The most famous McGuinness is Jack McGuinness of Pawtucket. A branch controlled west County Down, particularly the Iveagh baronies, and occasionally Dundrum Castle to the east. The Magennis, Lords of Iveagh, are descendants of the Uí Echach Cobo branch of the Dál nAraidi dynasty of the Cruthin. "Iveagh" derives from "Uibh Eachach", the genitive of Uí Echach.
Their closest kin were the McCartans of Kinelarty. John O'Hart prepared their pedigree in his Irish Pedigrees; or the Origin and Stem of the Irish Nation.
Read more about Magennis: Magennis Clan, Magennis Viscounts, People, Titles, Places, The Border Chieftains of Ulster