| Name | Gender | Pronounced | Usage | Popularity |
|---|---|---|---|---|
| Iago | ee-A-gaw (Welsh, Galician), ee-AH-go (English) | Welsh, Galician, Portuguese | ||
| Ianto | - | Welsh | ||
| Idris (2) | - | Welsh | ||
| Idwal | - | Welsh | ||
| Iefan | - | Welsh | ||
| Iestyn | - | Welsh | ||
| Ieuan | - | Welsh | ||
| Ifan | - | Welsh | ||
| Ilar | - | Welsh | ||
| Illtyd | - | Welsh | ||
| Ioan | - | Romanian, Welsh, Bulgarian | ||
| Iolo | - | Welsh | ||
| Iolyn | - | Welsh | ||
| Iorwerth | - | Welsh | ||
| Islwyn | - | Welsh |