I am researching the Carnahans also. A vast number are found in Allegheny and Westmoreland Counties. Mine are in Bucks County. Thomas is listed in the 1870 census of Falls Twp., Fallingston, PA. He is also listed as a farmer in the same area in the 1889 directory. Yes, there are MANY spellings and I'll list a few - Kernahan, Kernaham, Carnaham, Carnah, Carnochane, Caraghan, Carnoquhan, Carnaghan, Carnagan, Carnaughan and so on. I have no more in front of me at this time, but you can be assured that more exist.