I've spent quite a few hours looking in many places but I cannot find anything concrete - sorry.
However, this is what I think from what I have found and not found:
His parents were John T. McCoy (b. betw. 1812 & 1820) who married Martha E. Turner (b. 1818) in Troup Co. Georgia, 29 Mar 1843.
John's father was born in North Carolina - so John could have been born in N.C. - but his mother was born in Ga. which is my guess.
Dunkin served in the US Civil War. He could have been born in 1835 +/- 2 yrs.
These are my thoughts but are by no means correct.