terraria iron ore where to farm it?

Answer 1

 

Obviously, you cannot "farm" iron, you mine it. You can find iron ore in the ground near the surface or in caves and use it to make iron bars at a furnace.

Comments

You realise the term "farm" simply means to acquire large quantities of a certain object? Just because you say you're going to farm something, doesn't mean it actually involves farming in the agriculture sense.

---

No, I didn't realize that, so thanks.

Answer 2

You can gather large Quantities of Iron ore all over the map.

My recommendation is use a the Terraria Mapper to find it.

It will show the location of everything on the map. Including chests, ores, gems, water, lava, Hell and all biomes.