Hi there, there is always room for more answers, but it might be useful if you could narrow down your question a bit -- "the Americas" are a large place and "before colonization" is roughly 40,000-50,000 years.

To very briefly answer your question: yes, there was a very large Native American population in what we now call the Americas; the natives built large cities and complex ceremonial structures most famously in Mesoamerica, but also earth structures in what's the current-day United States and stone highways and monuments in South America. There were many hundreds of distinct groups with their own individual cultures.

However, as we await answers, you may be interested in this section of the FAQ:

http://www.reddit.com/r/AskHistorians/wiki/faq#wiki_americas_before_columbus_and_native_american_history

and specifically a few answers I pulled out that may interest you:

http://www.reddit.com/r/AskHistorians/comments/142fix/how_much_do_we_know_about_presettler_native/

http://www.reddit.com/r/AskHistorians/comments/1v5n7x/what_differences_caused_the_mesoamerican/

http://www.reddit.com/r/AskHistorians/comments/vxrv4/a_photo_on_my_facebook_showed_up_today_claiming/

http://www.reddit.com/r/AskHistorians/comments/12a3vk/we_all_know_how_there_was_a_huge_population/

Hope this helps!