Iron

Iron is currently used for crafting a lot of essential items.

Located:
Tor's Bane

Maui's Haven

Sea Spotter Isle

Isle of Lumpy

Skull Island

No Man's Land

Used in Crafting:
Advanced Workbench

Altar

Anvil

Bucket

Cannon

Cannonball

Cauldron

Chest

Cooking Pot

Hammer

Iron Axe

Iron Chestplate

Iron Helmet

Iron Leggings

Iron Pickaxe

Iron Shield

Iron Sword

Shovel

Sickle

Sledgehammer

Spiked Club

Steel