| English Surname | Original Irish Surname Male | Original Irish Surname Female Unmarried | Original Irish Surname Female Married |
| Uiske | Mac Conuisce | Nic Conuisce | Mhic Conuisce |
| Ultagh | Ultach | Ultach | Ultach |
| Umphrey | Unfraidh | Unfraidh | Unfraidh |
| Unehan | Ó hOnchon | Ní hOnchon | Uí hOnchon |
| Uniacke | Doinneard | Doinneard | Doinneard |
| Uprichard | a Priocaird | a Priocaird | a Priocaird |
| Upton | Uptún | Uptún | Uptún |
| Urrell | de Oirghialla | de Oirghialla | de Oirghialla |
| Usher | Uiséir | Uiséir | Uiséir |
| Mac Usker | Mac Oscair | Nic Oscair | Mhic Oscair |
| Ustace | Iústás | Iústás | Iústás |
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