For the record, this is every chest in the game. This includes ones found via Treasure Maps and the 5 each on the two Sky Islands. Treasure Maps can be found in specific areas and show as a golden "rare" supply point on your local map (see addendum, below, for locations). More chests will be added to the various regions at, or around, Chapter 12.
I only had some difficulty finding all of the chests in Crystal Canyon (they're hidden in crevices and within caves) and ONE chest in Emerald Town, which was all the way back in the grassy area behind the third, or fourth subdivision (from the left; it's near a tree by the water).
Added the following (very helpful) information by HATRED REMAINS:
Some of these you have to pick up, go to the location indicated and search for a yellow sparkle. (You have to have finished the 'Treasure Map' sidequest which is a storyline sidequest in Chapter 8).
Turtle Map: Crystal Canyon East Side. Treasure location: West of Sapphire Town above the beach in the Turtle-like cave.
Dragon Map: Cannon Island all the way North. Treasure location: Crystal Canyon at the top of the crystal structure.
Cloud Map: Aboard the Ship Wreck west of Sapphire Town. Treasure location: Law's Sky Island at the peak.
Waterfall Map: Luffy's Sky Island Northeast next to a chest. Treasure location: Behind the waterfall in Crystal Canyon.
Pond Map: Aboard the Pirate Ship in Ruby Village. Treasure location: The lone rock in the lake in the Graveyard.
Stepping Stones Map: You get this for doing the Ghost in a barrel sidequest (Ruby Village). Treasure location: Sea Prison - Aquamarine next to the bridge.
Boulder Map: Law's Sky Island North. Treasure location: On the mountain/cliff next to the Thousand Sunny.
Ruins Map: For finishing the 'Where's Buggy?' sidequest (You get it in Ruby Village after finding the Stepping Stones treasure). Treasure location: between 2nd and 3rd street Emerald Town.