Piercings in Cheonan
There's a store called "Artbox" in Cheonan that does piercings. It's on a side-street, right next to the CGV Movie Theater. If you're walking down the main road from downtown to Cheonan-yeok, keep walking past the train station and turn left at Baskin Robbins and you'll find it on your left hand-side.
I got my eyebrow pierced for 10 000 won. You'll have to stop by the store for more information about other stuff, I didn't ask.