America's First Banned Book
atlasobscura.com
atlasobscura.com
Also, it seems that in the 15th century Itzcoatl, a Mexica tlatoani, ordered the burning of many historical codices. I was not able to find earlier instances of banned books. Also, I do not know whether Indians in what is now the US or Canada had books (that could then be banned).
It does make me wonder what the world would have looked like today, had Morton and his allies won out against the puritans. He was still old world money after all, and could have anchored commerce in Britain's interest. Very likely the "New World" would be under British rule, or perhaps would have rebelled at a later point in time.