| Innocentius | | - | Late Roman | |
| Iosephus | | - | Late Roman | |
| Isaura | | ee-SOW-rah (Spanish) | Portuguese, Spanish, Late Roman | |
| Isaurus | | - | Late Roman | |
| Isidorus | | - | Late Roman | |
| Iucunda | | - | Late Roman | |
| Iustina | | - | Late Roman | |
| Iustinianus | | - | Late Roman | |
| Iustinus | | - | Late Roman | |
| Iustus | | - | Late Roman | |
| Jacobus | | yah-KO-bus (Dutch) | Dutch, Late Roman | |
| 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 | |
| Justina | | jus-TEE-nə (English) | English, Slovene, Czech, Lithuanian, Late Roman | |