As who I believe to be Flem's father is the second husband of who I believe to be in my ancestoral line I have no proofs but the circumstaintial evidence is such that I think it will prove to be a very good lead for you. I don't imagine there were too many Fleming Gent's. Campbell Gent and Priscilla Sheldon Hood Gent (the Hood is mine) had at least two children. Their names were Fleming born abt. 1842 and Lucy born 1844. Both were born in Ohio. Sometime between 1846 (when Priscilla died in Scioto County Ohio) and 1850 (when Lucy can be seen living with her grandparents in Massac County ILL) they moved from Ohio to Ill. Go to censusonline, click ILL then Massac County. About half way down page 240a are Richard and Abigail Sheldon with granddaughter Lucy Gent staying with them. I'm STILL trying to figure out where Fleming was during this time. He MAY have been living with a local farmer or other business man learning a trade. Priscilla died in 1846 (in Ohio) and Campbell remarried in 1846 (in Ill). Then, in 1848Campbell's wife, Almeda, remarries. This leads me tobelieve that Fleming and Lucy were orphaned by 1848.
If you've found the 1880 census for Fleming you'll notice he said his mother was born in Ohio. An easy mistake for a boy to make when he was orphaned so early (about age 4), knew he had lived in Ohio when young, and his mother had died there. Actually, unless your's is another Fleming Gent who was born in Ohio the right year and ended up in Ill with his father and grandparents too, his mother was from New Jersey.
Sooo, to give you the "Reader's Digest Condensed Version" (did I just show my age?), I believe Fleming to be the son of Campbell Gent born in Lawrence County Kentucky and Priscilla Sheldon born in New Jersey. I have a copy of the page of the 1840 census on which Campbell is listed if you'd care to have it. He is listed with another male, William Gent, and two children who may be his or William's. I never troubled to find out as I'm having a hard enough time with my elusive Hood line!
Hope this helped in some way. Let me know if you have any questions either about the content of this posting or questions in general. Maybe the answer's in my Sheldon notebook!