From an upcoming paper on genetics. This should be headline news:
“[A] large wave of German immigrants are known to have settled in Pennsylvania before 1780-1810, and tended not to move once they settled there. We detect not one but three distinct subgroups that settled in slightly different parts of Pennsylvania. We can trace their ancestry from different parts of Germany and Switzerland at that time and confirm it through aggregating estimates of their ancestry based on their genomes and common surnames found in their pedigrees.”
They’ve identified other American ethnic groups too. We’ll have to wait for the paper to be presented (early October) to see what they have.