How many North American Indians were killed by European colonists and the US Army?

The US did not keep records of how many individuals it killed, unlike the Germans, Serbians, and Soviets. Furthermore, consider that the first Europeans likely arrived in North America in the 13th century in the form of Vikings. So it's been about 800 years. If you're looking for anything resembling a close approximation then you're going to be left disappointed.