| # | Name | Origin | Meaning | Gender | |
|---|---|---|---|---|---|
| 541 | Huey | Welsh | Variant of the Latin Hugh. A thinker. Intelligent. | M | |
| 542 | Hugh | Welsh | Variant of the Latin Hugh. A thinker. Intelligent. | M | |
| 543 | Hughie | Welsh | Variant of the Latin Hugh. A thinker. Intelligent. | M | |
| 544 | Huw | Welsh | Welsh form of Hugh. A thinker. Intelligent. | M | |
| 545 | Hydd | Welsh | Deer. | M | |
| 546 | Hywel | Welsh | Eminent. | M | |
| 547 | Iago | Welsh | Supplanter. Can be either a variant of James or Jacob. Associated with the wicked Iago in Shakespeare's Othello'. | M | |
| 548 | Iau | Welsh | Welsh form of Zeus 'life'. | M | |
| 549 | Iddawg | Welsh | Legendary son of Mynyo. | M | |
| 550 | Iddig | Welsh | Legendary son of Anarawd. | M | |
| 551 | Idella | Welsh | Bountiful. | F | |
| 552 | Idris | Welsh | Fiery lord. | M | |
| 553 | Ifor | Welsh | Lord. Can also be a variant of Ivor. | M | |
| 554 | Indeg | Welsh | Legendary daughter of GanKy. | F | |
| 555 | Ioan | Welsh | Welsh form of John 'God's gift'. | M | |
| 556 | Iob | Welsh | Diminutive of Iorwerth: Worthy lord. Derived from 'ior' and 'gwerth'. Legendary son of Maredudd. | M | |
| 557 | Iola | Welsh | Valued by the Lord. Feminine form of Iolo: Diminutive of Iorwerth. | F | |
| 558 | Iolo | Welsh | Diminutive of Iorwerth: worthy lord. | M | |
| 559 | Iona | Welsh | Legendary king of France. | M | |
| 560 | Iorwerth | Welsh | Worthy lord. Derived from 'ior' and 'gwerth'. Legendary son of Maredudd. | M | |