How do you find the last trinket in Assassins Creed 3

Edit- I purchased the full trinket map and collected every trinket that the map indicated, but the game still says that there is one more trinket that I need to collect before the big treasure is unlocked. Does anyone know where the trinket is? Does the map not unlock everything?

I am 52% of the way through the game and checked every area that I have unlocked- The Homestead, the Frontier, Boston and New York.