"The population figure for indigenous peoples in the Americas before the 1492 voyage of Christopher Columbus has proven difficult to establish. Scholars rely on archaeological data and written records from settlers from the Old World. Most scholars writing at the end of the 19th century estimated the pre-Columbian population as low as 10 million; by the end of the 20th century most scholars gravitate to a middle estimate of around 50 million, with some historians arguing for 100 million or more." - that's for both North and South America.
https://en.wikipedia.org/wiki/Population_history_of_indigeno...
But there is recent genetic evidence that a severe narrowing of genetic diversity happened across the continent. And a fairly recent one.
Out of curiosity, why do you word it this way? I'm curious because I have a coworker that thinks the smallpox story is some evil liberal conspiracy of some sort, and never happened. Yet I see only evidence for, not against.