I see a lot of people on the internet claim there were 90 to 100 natives living in the U.S. pre-colonization, but I'm pretty sure that number is what the estimated population of North and South America was at the time, correct? Does anyone have any idea roughly what the number was inside the actual United States?
Let me just start by saying I am by no means an expert on Native American history and I'm sure someone can give you a much more thorough and accurate answer.
90 to 100? If you mean thousand, the figure would be far north of that. No one has a firm grasp on how many Natives actually lived in the Americas before Columbus, but figures range wildly from low millions to tens of millions. We do know that the native population was around 6 million in 1650. This was largely due to disease, warfare, and colonization.
The consensus among many scholars is that as much as 90% of the native population died due to disease brought by European colonizers. This phenomenon is sometimes known as or connected to the American Indian Genocide; although my personal beliefs are that genocide might be too harsh a term considering colonizers at the time had no idea they were exposing natives to incredibly deadly disease that they had no immunization to. This makes it incredibly difficult to gauge the number of natives living in the Americas before they were colonized.
There's a book out there called American Indian Holocaust & Survival which estimates between 2 and 18 million, but if I'm remembering correctly, I think the book is pretty old so I'm not sure if the figures are up to date with current theories
EDIT: I just found /u/400-Rabbits posts from a few years ago
Post 2: https://www.reddit.com/r/AskHistorians/comments/2sx6h9/whats_the_current_scholarly_consensus_of/
I am also not an expert on the field by any means, but I started reading a book called North American Indians: A Very Short Introduction by Theda Perdue and Michael D. Green. Both of the authors have been teaching and writing about American Indians for nearly 40 years and are both acclaimed scholars on this topic. In this book, meant to give a brief introduction into the field of Native American Studies, they estimate that there were approximately five to seven or eight million people when Columbus arrived in North America. The population estimates are inexact at best, yet I would go with the 5-8 million people range.