> I think that the 1700s are really the launching point for the ballad history in America.

I'm inclined to agree, and later in the century rather than earlier.

That's not to deny that ballads were presumably sung earlier. But recall that the U.S. population in 1790, from Georgia to Maine, was under 4 million (compared with 92 million in 1910, the census prior to Sharp's visit). The entire Anglo-Celtic population, the group likely to be singing Child ballads, was probably no more than 3 million. (There were 700,000 Negro slaves in 1790.)

Southern Appalachian state populations in 1790:

Virginia: 748,000
Kentucky: 74,000
N. Carolina: 374,000
S. Carolina: 250,000
Georgia: 83,000

Roughly half a million of those counted were slaves (who may have been unlikely to sing Child ballads). There were not a whole lot more people living in all of the Southern Appalachian states in 1790 than are living in Phoenix today.

I haven't checked on the Appalachian numbers for 1910.

It may well be that many more people in 1790 knew many more ballads than in 1910, but for all we know the opposite may have been the case. There's no way to correlate the small population and the greater difficulty of travel in the 18th C. with ballad singing, but it seems at least possible that fewer people, greater distances, greater isolation from printed sources, and fewer social networks made for fewer ballads and ballad performances.

Only a suggestion.