| Birth | Nov 1849 | Illinois | | | |
| Census | 1 Jun 1850 | Twp. not listed, Williamson Co., IL, stamped pg. 293B, actual enumeration date 14 Dec 1850; Thomas B. Duncan, 8/12, born IL. (Sep 1849 if based on official date or Mar 1850 if based on actual date of enumeration.) | | | |
| Census | 1 Jun 1860 | P.O. Marion, Twp 8 Range 2 E, Williamson Co., IL, pg. 147; Thomas Duncan, 11 (1848-49), born IL. | | | |
| Marriage | 24 Nov 1871 | Williamson Co., Illinois - Elizabeth J. SOWELL | |  | |
| Census | 1 Jun 1880 | Twp. 8 Range 3 East, Lake Creek, Williamson Co., IL, ED 158 pg 39; Thomas Duncan, head, 31 (1848-49), born IL both parents born IL, farmer. Married. 2 houses from Sowell family. | | | |
| Census | 1 Jun 1900 | Lake Creek Pct., Williamson Co., IL, ED 116 Sh 3A; Thomas B. Duncan, head, born Nov 1849, 50, married 28 yr., born IL both parents born IL, farmer. | | | |
| Census | 1 Jan 1920 | Herrin, Williamson Co., IL, ED 174 Sh 7B; Thomas B. Ducan [sic], head, 70 (1849), born IL both parents born IL, farmer. Son "Leaman" next door. | | | |
| Death | Aft 1 Jan 1920 | | | | |
| Reference No | | 7255 | | | |