Surname I - J
| SURNAME | TOWNSHIP | RESEARCHER |
| Immenga | Linda Shooks | |
| Immenga | Wauconda | Carol Girvin |
| Isaachsen | Kathi Turner | |
| Jackson | Chicago & Surrounding area | Linda Defalco |
| Jacobson | Grayslake & Waukegan | Cheryl Peterson |
| Jahnke | Barrington | Meg Jahnke |
| James | Antioch | Lee Koenig |
| Janssen | Antioch, Grant, Avon, Shields | Terri Miller |
| Jarmuth | Verdell Leikam | |
| Jenkinson | Waukegan 1853-1940s | Philip Smith |
| Jones | 1850-1900 | Bill Jones |