I have not found confirmation of birth place for Pop Pop.
On all the census records, his birthplace is listed as Ohio. Since he is living in Granville, Ohio at age 2. I think that's a pretty good 1st guess.
Though you are correct, of course, that we don't have any "proof" yet. :)
I will agree with your pretty good first guess!
I love seeing research, documentation, and deduction at work -- collaboration at it's best!