One of the main shopping areas in Ilsan is an outdoor mall type area called 'La Festa'. And it's here that you can find all of the major Korean chain store type beauty shops. You can find these stores all over Korea as they are very popular and many of them have more than one branch in most areas.
These shops are all within a stretch of two blocks and many of them are just right next to each other.
There are also a couple more just a little bit along the street from these ones but I didn't get photos of them, They are called Watsons and Olive Young and are more Pharmacy/Drugstore type shops with lots of different brands and products. Here in Korea however they don't carry the medicine that you get in many of these type stores in Western countries. They have specific stores that sell medicine and those don't really sell anything else, just health related products.