| # | Name | Origin | Meaning | Gender | |
|---|---|---|---|---|---|
| 641 | Tadhg | Gaelic | Poet. | M | |
| 642 | Taggart | Gaelic | Son of a prelate. | M | |
| 643 | Taidhg | Gaelic | Poet. | M | |
| 644 | Taithleach | Gaelic | Quiet. | M | |
| 645 | Teague | Gaelic | Poet. | M | |
| 646 | Tearlach | Gaelic | Manly. | M | |
| 647 | Tearley | Gaelic | Manly. | M | |
| 648 | Tearly | Gaelic | Manly. | M | |
| 649 | Teimhnean | Gaelic | Dark. | M | |
| 650 | Terrence | Gaelic | From the knolls. | M | |
| 651 | Thornton | Gaelic | Town of thorns. Thorn variants are English surnames occasionally used as given names. | M | |
| 652 | Tioboid | Gaelic | Bold. | M | |
| 653 | Tomas | Gaelic | Twin. | M | |
| 654 | Tormod | Gaelic | From the north. | M | |
| 655 | Torrance | Gaelic | From the knolls. | M | |
| 656 | Tuathal | Gaelic | Peaceful. | M | |
| 657 | Tulley | Gaelic | Peaceful. | M | |
| 658 | Tully | Gaelic | Peaceful. | M | |
| 659 | Tynan | Gaelic | Dark. | M | |
| 660 | Uilleam | Gaelic | Helmeted. | M | |