| Isokrates | | - | Ancient Greek | |
| Iudicael | | - | Ancient Celtic | |
| Iudocus | | - | Ancient Celtic (Latinized) | |
| Iulia | | YOO:-li-a (Ancient Roman) | Romanian, Ancient Roman | |
| Iuliana | | - | Romanian, Ancient Roman | |
| Iulianus | | - | Ancient Roman | |
| Iulius | | YOO:-li-uws | Ancient Roman | |
| Iunia | | - | Ancient Roman, Biblical Latin | |
| Iunius | | - | Ancient Roman | |
| Iuvenalis | | - | Ancient Roman | |
| Ivo (1) | | EE-vo (German, Dutch, Italian), EE-fo (German), EE-voo (Portuguese) | German, Dutch, Italian, Portuguese, Czech, Ancient Germanic | |
| JÓRunnr | | - | Ancient Scandinavian | |
| Januarius | | - | Ancient Roman | |
| Jarl | | YAHRL (Norwegian, Swedish, Danish) | Norwegian, Swedish, Danish, Norse Mythology, Ancient Scandinavian | |
| Jodocus | | yo-DO-kəs (Dutch) | Dutch (Archaic), Ancient Celtic (Latinized) | |