I finally found proof of Thornton Davis’s father after 2 years of searching! His name was John Davis Sr. His estate was administered in Abbeville in 1826. I found his estate papers on Ancestry.com by accident. The estate papers mention William, Melinda, John, and Thornton. William Davis was administrator so he was probably the eldest son. The estate sale was held at Pleasant Grove Meeting House.
Many people listed in the estate papers of John Davis are the same people listed in the estate papers of Thomas Donaldson in 1811. There was probably a mutual connection between John and Thomas. Thornton Davis married the daughter of Thomas, Sally Cook Donaldson, in 1816.
Another thing I found interesting is that John Davis had a daughter Melinda. There is also James Cook listed several times in the estate papers. There is a Lindy Cook mentioned in Cornelius Cook Jr’s estate paper of 1838 along with his brother James Cook. I wonder if Lindy was in fact Melinda Davis.
*The estate record is in Box 27, Pack 612