There are a total of 172 chests throughout the map (use in game count not XB hub) and while this is not a guide to finding them, I felt the need to write something so people might be less discouraged if they perhaps knew something about post game cleanup.
During the 3 green moon quest, you'll be given a treasure tracker which beeps as you get closer to a chest. After you beat the final boss, your home town will gain 3 more items to buy from the vender, one of which tells you how many chests are left in the game. You will also gain upgrades to increase the range at which it can detect treasures. At that point it becomes just a matter of walking around in each area listening for beeps, and searching high and low as well as inside any small crack you might see just to find those treasures. Some are literally at the top of the maps (or Swords, Ya that one) where most people can't even get to without
as well as a few are out in the out of bounds area's like behind the blue castle down a long hallway of water which you need to Spiderman to get (purple gun rope jumping @ don't break your controller).
*At the end of the chest collecting, just for those that want to see matching stats. I'd take a screen shot but the game brings up the pause menu before you can actually get it to take one.
Armour 3 HP 200
Moon"super" Sword 79
Red Gun 79/128/300
Teleport Gun 400
Force Cube 90
I'm sure you can find video guides and pictures of where each one is, but trust me it's easier to get what you can early as you play and then just use the treasure tracker to find the rest, it goes so much quicker than looking up each one via picture.. The only challenge comes from trying to find where the beep is telling you it is, which is why I say even the smallest of cracks might be where you need to go (teleport).