My family tree (ancestry.com, myheritage.com) locates my 4XG Grandfather (Thomas Reid) in Cumberland, Allegany County, Maryland. In 1803, he married Mary "Polly" Kershner. The 1810 US Census shows the family living on Mechanic Street. There are three children: one girl and two boys. There are also two males aged sixteen to twenty. (I have no idea who these boys might have been.) In 1819, Thomas died.
The 1820 US Census shows Mary living with her father (Michael Kershner). When Michael's will is probated, it names his Reid grandchildren: George M., Ann, Thomas H., Peter, James and Cecelia. In 1824, Mary married John Johnson (from Bedford County, Pennsylvania), having two more children by him: Emanuel and Samuel.
So my "brick wall", for over twenty years, has been finding the parents of Thomas.
Among the Scotch-Irish of this era, the first-born son was named after his Paternal great-grandfather and his grandfather. I believe Thomas's first born son did not survive his father. I believe George named his first born son in accordance with this custom and therefore reveals in this name, John Thomas Reid, the name of Thomas's father. But, I have no proof.

The "Brick Wall" still stands!