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| Guinness | fairly rare: Belfast area and scattered. Ir. Mac Aonghuis, from early personal name Aonghus, Óengus. A sept of Down. See MacGuinness, Magennis. IF. |
| Mac Aonghusa | rare: Dublin etc. Ir. Lang. See Mac Guinness. |
| MacEnnis | Very rare: Limerick. See Mac Guinness. |
| MacGennis | Very rare: Dublin. See Magennis. |
| MacGinnis | Derry etc. Ir. Mag Aonghuis. See Mac Guinness. |
| MacGuinness | Very numerous: all areas, especially Ulster, Connacht, N Leinster. Ir. Mag Aonghusa, Mag Aonghuis. From legendary first name Óengus. A leading sept of Ulster, chiefs of Uíbh Eathach (Iveagh) in Down. Perhaps now most celebrated for the dark beer. |
| Magenniss | numerous: Down-Armagh etc. Ir. Mag Aonghusa. Variant of Mac Guinness, q.v. |
| Maginess | fairly rare: Down-Armagh. See Mac Guinness. |
| Maginnes | fairly numerous: Belfast, Down-Antrim etc. Ir. Mag Aonghusa. Variant of Mac Guinness, q.v. |
| Maguinness | rare: Down etc. Variant of Mac Guinness, q.v. |
Parishes where a Maginess and a second surname married each other.