| SURNAME | TOWNSHIP | RESEARCHER |
| Tattler | Diamond Lake, left area ca 1903 | Wendy Goldfein |
| Taubel | Antioch | Denise Parsons |
| Taylor | died ca 1850-1853 | Tom Taylor |
| Tazewell | Mary Lou Heal Gdowski | |
| Tekampe | Bob Tekampe | |
| Thayer | Rita Breeding | |
| Theivagt | Elisabeth Forbes | |
| Thielen
website |
Jim Thielen | |
| Thompson | Lyla Weinreber | |
| Thoms | Shirley M. Cummings | |
| Thoms | Lake Zurich, Barrington; 1880s-1950s | Peggy Doyle |
| Tiernan
website |
Waukegan | Terri Tiernan Maguire |
| Towner | Mary Towner Hansen | |
| Traut | Lisa Traut | |
| Triggs | Shields/Vernon/Libertyville | Marleen Van Horne |
| Trotter | Sophia Preston | |
| Tucker | Fremont Twp. | Carolyn Caflisch |
| Tyrrell | Waukegan, ca 1850s - ca 1950 | Phil Smith |