| # | Name | Origin | Meaning | Gender | |
|---|---|---|---|---|---|
| 381 | Hugh | Welsh | Variant of the Latin Hugh. A thinker. Intelligent. | M | |
| 382 | Hughie | Welsh | Variant of the Latin Hugh. A thinker. Intelligent. | M | |
| 383 | Huw | Welsh | Welsh form of Hugh. A thinker. Intelligent. | M | |
| 384 | Hydd | Welsh | Deer. | M | |
| 385 | Hywel | Welsh | Eminent. | M | |
| 386 | Iago | Welsh | Supplanter. Can be either a variant of James or Jacob. Associated with the wicked Iago in Shakespeare's Othello'. | M | |
| 387 | Iau | Welsh | Welsh form of Zeus 'life'. | M | |
| 388 | Iddawg | Welsh | Legendary son of Mynyo. | M | |
| 389 | Iddig | Welsh | Legendary son of Anarawd. | M | |
| 390 | Idris | Welsh | Fiery lord. | M | |
| 391 | Ifor | Welsh | Lord. Can also be a variant of Ivor. | M | |
| 392 | Ioan | Welsh | Welsh form of John 'God's gift'. | M | |
| 393 | Iob | Welsh | Diminutive of Iorwerth: Worthy lord. Derived from 'ior' and 'gwerth'. Legendary son of Maredudd. | M | |
| 394 | Iolo | Welsh | Diminutive of Iorwerth: worthy lord. | M | |
| 395 | Iona | Welsh | Legendary king of France. | M | |
| 396 | Iorwerth | Welsh | Worthy lord. Derived from 'ior' and 'gwerth'. Legendary son of Maredudd. | M | |
| 397 | Ithel | Welsh | Generous lord. | M | |
| 398 | Iustig | Welsh | Legendary son of Caw. | M | |
| 399 | Ivor | Welsh | Variant of Ifor: Lord. Can also be a variant of Ivor. | M | |
| 400 | Iwan | Welsh | Welsh form of John 'God's gift'. | M | |