Amy, there is a Patricia Hamill on Ancestory.com who found a lot of info from a book by Goodspeed called "History of Tennessee." You may be able to find it in your public library. Do you live in Chattanooga? I was very serious about attending a Hamill reunion. If you have any info on that, please let me know.
I also ran across a listing of all government officials from the 1700's and 1800's for Hamilton County/Chattanooga and a Hamill (forgot first name) served as a Registrar. Was your great grandfather a gov't official?