It is often believed that the Americas were sparsely populated. Some estimates of the population in Hispaniola (the island that Columbus landed in) was only a mere 100,000 - 120,000.
The exact number is difficult to find for certain. After the Europeans arrived, disease and war wiped out a large number of natives which makes it hard to count the population before they arrived. Some counts during the time were also disregarded by historians of the time. They thought that the people living there were too primitive to have such a large population and cut the numbers down to what they believed to be more appropriate.
The original 100,000 guess was made using the same evidence as an 8 million people estimate made in the past 50 years. These numbers were both based on the same census of the island (Denevan, xxiii).
Even more conservative modern estimates believe that the population was over 1,000,000 by the time Columbus arrived at the island.
As for the entire population in the Americas at the time, estimates vary from 54-112 million. These numbers are still impressive considering the population of Europe at the time was about 40-70 million (Britannica).
Regardless of what the actual numbers are, the high estimates help prove that the Americas were more developed than some may originally thought.