That 12 million is only a fraction. Most immigrants did not come through Ellis Island. My ancestors didn’t. They apparently transferred from a big boat to a small boat and rowed up the river into PA.
Up through free market Coolidge there was no such thing as an “undocumented” or “illegal” immigrant. It was only in the late 20s with RINO Hoover that a law was passed to make it a mis-demeanor to enter the US without playing Mommy-May-I with the Feds. As with Smoot-Hawley, RINO Hoover had to placate factions of populist Republicans while moving toward big government. Big government in immigration was part of his Big government agenda.
bump
There were people forbidden to come to the U.S. and there were smugglers of illegals, this was in the 1800s, so there were illegal immigrants.