Thank you for posting all the information about George and his descendants.I think I have two things to contribute.
First, I think I found George in the 1820 census.I used Heritage Quest, an electronic database (that has its fair share of errors) and, indexed as "Dwinny" was a George.When I actually looked at the image, however, it seemed to be either Devinney or Davinney.This George had statistics as follows:
Davinney, George Md Cecil 2-Dist 1820 4-1-0-1-0-1;0-0-0-1-1
In addition, in 1817, one William Jameson of North Milford Hundred, Cecil County, executed a will and used a man named Devinney as one of three witnesses.The other two witnesses were a Moses Scott and a John R. Giles.I believe this witness might have been George Devinney.
You have analyzed census statistics and I believe you have estimated that George Devinney Sr. was born before 1740-1750?Do you know when he died?He seems to be in the 1810 census but not the 1820 census.If he died before 1817, then he could not have witnessed the Jamesson will, and it would have been one of his sons, instead.
I am exploring the hypothesis that there might have been some connection stronger than "neighbor" between the Devinney family and the Jameson famiy.Any ideas?You can contact me directly at firstname.lastname@example.org if you wish.