When I’m looking at Census statistics, I sometimes see people giving their ancestry as “American” or “USA”. It seems to be most common in the South. What does this mean?
Ancestry for the census is completely self-identified. You can write anything you want.
So people can say that their families have been here long enough that their ancestry is “American.” Or they can do it because they’re chauvinist. Or because they don’t know any better. Or don’t know who their ancestors are. Or for any reason at all, really.