| Iustina | | - | Late Roman | |
| Iustinianus | | - | Late Roman | |
| Iustinus | | - | Late Roman | |
| Iustus | | - | Late Roman | |
| Iuvenalis | | - | Ancient Roman | |
| Jacobus | | yah-KO-bus (Dutch) | Dutch, Late Roman | |
| Januarius | | - | Ancient Roman | |
| Janus | | - | Roman Mythology | |
| Joannes | | - | Late Roman | |
| Johanna | | yo-HAH-nah (German), yo-HAHN-nah (Danish, Dutch), YO-hahn-nah (Finnish) | German, Swedish, Norwegian, Danish, Dutch, Hungarian, Finnish, Estonian, English, Late Roman | |
| Johannes | | yo-HAH-nes (German), yo-HAHN-nəs (Dutch, Danish), YO-hahn-nes (Finnish) | German, Dutch, Swedish, Norwegian, Danish, Finnish, Estonian, Late Roman | |
| Jove | | JOV (English) | Roman Mythology (Anglicized) | |
| Jovian | | - | Ancient Roman (Anglicized) | |
| Juliana | | yuy-lee-AH-nah (Dutch), yoo-lee-AH-nah (German), joo-lee-AHN-ə (English) | Dutch, German, English, Spanish, Portuguese, Ancient Roman | |
| Julius | | YOO:-li-uws (Ancient Roman), JOO-lee-əs (English), YOO-lee-uws (German) | Ancient Roman, English, German | |