| Junia | | - | Biblical, Ancient Roman | |
| Junius | | - | Ancient Roman | |
| Juno | | JOO-no (English) | Roman Mythology | |
| Jupiter | | JOO-pi-tər (English) | Roman Mythology (Anglicized) | |
| Justina | | jus-TEE-nə (English) | English, Slovene, Czech, Lithuanian, Late Roman | |
| Justus | | YUWS-tuws (German), JUS-təs (English) | German, Dutch, Late Roman | |
| Juturna | | - | Roman Mythology | |
| Juventas | | - | Roman Mythology | |
| Katerina | | - | Macedonian, Russian, Bulgarian, Greek, Late Roman | |
| Kay (2) | | - | Welsh Mythology, Arthurian Romance | |
| Laelia | | - | Ancient Roman | |
| Laelius | | - | Ancient Roman | |
| Laetitia | | - | Late Roman, French | |
| Lancelot | | LAN-sə-laht (English) | Arthurian Romance | |
| Lara (2) | | - | Roman Mythology | |