| Birth | Bet Dec 1848 and 1849 | Illinois | | | |
| Marriage | 26 Jan 1868 | Williamson Co., Illinois - John W. DUNCAN | |  | |
| Census | 1 Jun 1870 | P.O. Marion, Twp 9 Range 3 E, Williamson Co., IL, pg. 11; Mary C. Duncan, 21 (1848-49) born IL. | | | |
| Census | 1 Jun 1880 | Lake Creek, Twp 8 Range 3 E, Williamson Co., IL, ED 158 pg 23; Mary C. Duncan, wife, 30 (1849-50), born IL both parents born TN. | | | |
| Census | 1 Jun 1900 | Lake Creek, Williamson Co., IL, ED 116 pg 6B; Mary C. Duncan, head, born Dec 1849, 50, widow, mother of 12, 8 living, born IL both parents born TN, farmer. Next door to Isaac Atwood. | | | |
| Census | 15 Apr 1910 | Lake Creek Twp., Williamson Co., IL, ED 166 Sh 5B; Mary C. Duncan, mother-in-law, 60 (1849-50), widow, born IL both parents born TN, no occupation. Living with daughter Lulu Crain and her family. | | | |
| Census | 1 Jan 1920 | Marion City, East Marion Twp., Williamson Co., IL, ED 168 Sh 14A; Mary Duncan, mother-in-law, 70 (1849), widow, born IL both parents born TN. | | | |
| Census | 1 Apr 1930 | Marion City, West Marion Twp., Williamson Co., IL, ED 27 Sh 4A; Mary C. Duncan, mother-in-law, 80 (1849-50), widow, born IL both parents born IL [sic]. | | | |
| Reference No | | 7261 | | | |