How many Europeans emigrated to the Americas between 1820 and 1930?

How to get close to this number

Anchor on a single port. This site's Ellis Island question puts twelve million through one processing station over six decades. That station handled a large share of arrivals to one country, so a figure covering all of the Americas across a longer window has to be several times larger — which brackets the answer in the tens of millions.

The word "voluntary" in the description is doing significant work, and it is worth pausing on. Larger forced migrations happened across the same ocean in earlier centuries, and describing this as the largest migration in history without the qualifier would be wrong. Superlatives in migration statistics almost always carry a hidden category boundary.

The per-country shares in the explanation are more informative than the total. Several European countries sent an enormous fraction of their own populations, which reshaped the sending societies as much as the receiving ones — a fact that is easy to miss when migration is discussed only from the destination's point of view.