| Isolde | | i-ZOL-də (English), i-SOL-də (English), ee-ZAWL-du (German) | English (Rare), German, Arthurian Romance | |
| Israel | | IZ-ray-əl (English), IZ-ree-əl (English) | Jewish, English, Biblical, Biblical Greek | |
| Issac | | IE-zək | English | |
| Issy | | - | English | |
| Ivonette | | - | English (Rare) | |
| Ivor | | IE-vawr (English), EE-vawr (English) | Irish, Scottish, Welsh, English (British) | |
| Ivy | | IE-vee | English | |
| Izabelle | | IZ-ə-bel | English (Modern) | |
| Izzy | | IZ-ee | English | |
| Jace | | JAYS | English | |
| Jaci | | - | English | |
| Jacinda | | - | English (Rare) | |
| Jacinth | | JAY-sinth, JAS-inth | English (Rare) | |
| Jack | | JAK | English | |
| Jackalyn | | - | English (Rare) | |