Currency rates are subject to change and changes on the daily. So definitely keep your eyes out for it. Currently as of today (March 30, 2015) $1.00 USD = 1107.36 Korean Won
Check out the information below from VisitSeoul.net
There are 1,000; 5,000; 10,000; and 50,000 won bills. Coins come in 1, 5, 10, 100, and 500 won.