I'm going to go about this with prevalence in blonde hair. Greece which the most south eastern european country should have the least amount of blonde hair since we've been in the mediterranean climate the longest and unlike everyone else in Europe we haven't had any additional inflow of german or slavic peoples into the racial stock. Taking all that into account the demographic study shows that 11% of the total population is naturally blonde.
America seems to be at 2% naturally blonde now, HOWEVER, the US racial stock is northwestern European which means it should have a much higher percentage and that it couldn't naturally be as low as Greece but I'm using it as the bare minimum frequency for white people. America has 331 million people, 2% of that is 6.620.000 which means that there are actually be about 66.200.000 whites in the US instead of 204,277,273 whish is the US census claim.
Now obviously everyone has seen blonde americans who were clearly mixed or of terrible and uncertain racial stock, those that americans call white trash, if we remove those and the jews with blonde hair, let's say that only a tenth of ashkenazi jews have blonde hair, in a generous estimate there's 4,5 million purely white blondes ie
45 million pure white Americans.