Among the thousands of surnames being used by families here in the United States there are tons of truly ancestral last names and a bunch of fakes adopted by immigrants so they'd sound more "American".
Many of the real last names link families back to their European ancestry, which makes tracing their lineage fairly easy since the surnames are still being used in Europe to this day.
As you can see on the map above, posted by Redditor Teepr back in 2014, the most common European surnames are largely just what you'd expect- the Smiths are still a band in the U.K., Papadopoulos is still as Greek as it gets, and the Mullers are still amassed in Germany and Switzerland.
But, as this updated map posted by educational blogger Jakub Marian shows, there's a bit of a discrepancy when it comes to which last name is most common in Portugal.
The map above says Almeida is most common, but every other source seems to indicate Silva is actually the most common Portuguese last name.
Considering how many people of Portuguese ancestry in Latin and South American countries have the last name Silva I'm inclined to believe it's actually the winner.