I think I might be able to help you with some infomation.My grandmother's mother Sara Manring Thomas is related to the Thomas in Radnor, Ohio.
I grew up in Delaware on the outskirts of town, and believe me Radnor is SMALL!
Anyhow, what she says she was told is that the Thomas's, Manring's, and Knox's came to the US from Wales.They settled in Radnor.They established a Welsh church.But they really didn't like it becasue the land is very flat little tress not at all like Wales.
Some of the Thomas's then Manring's went south in Vinton County, Jackson County and wrote back that it was just like wales.Lots moved there.As a matter of fact, you should look for Thomas's in Gallia Ohio, Vinton and Jackson.
I am looking for the parent's of Albert Thomas. (connected to Radnor)Did David and Margret have children?
If you like, I could go to the cemetray for you. (It's not far from my home) and verify at the cemetary and the Ohio Historical Society for you.(Heck be kinda cool fora grave rubbing too for you!)