where to find terraria world file?

Answer 1

Go into search, Search "Terraria". It should be called "World1.wld", there may be a backup called "World1.wld.bak". Use the other one.

Comments

You can also go to My Games in My Documents folder.
You will find it there using Windows 7 :
"C:\Users\[Your computer username]\Documents\My Games\Terraria\Worlds"