| # | Name | Origin | Meaning | Gender | |
|---|---|---|---|---|---|
| 441 | Hefeydd | Celtic | Mythical father of Rhiannon. | M | |
| 442 | Heilyn | Celtic | Mythical son of Gwyn. | M | |
| 443 | Henbeddestr | Celtic | Fastest man. | M | |
| 444 | Henwas | Celtic | Mythical brother of Henbeddestr. | M | |
| 445 | Herne | Celtic | Mythical hunter god. | M | |
| 446 | Huarwar | Celtic | Mythical son of Halwn. | M | |
| 447 | Hueil | Celtic | Mythical son of Caw. | M | |
| 448 | Idelisa | Celtic | Bountiful. | F | |
| 449 | Idelle | Celtic | Bountiful. | F | |
| 450 | Iden | Celtic | Wealthy. | M | |
| 451 | Inness | Celtic | From the island. | M | |
| 452 | Innis | Celtic | From the island. | M | |
| 453 | Iona | Celtic | From the king's island. | F | |
| 454 | Ione | Celtic | From the king's island. | F | |
| 455 | Irven | Celtic | White. | M | |
| 456 | Irvin | Celtic | White. | M | |
| 457 | Irving | Celtic | White. | M | |
| 458 | Irvyn | Celtic | White. | M | |
| 459 | Isold | Celtic | The fair. | F | |
| 460 | Isolda | Celtic | The fair. | F | |