There are more Christians in South Korea (the Republic of Korea) than in other asian countries such as China and Japan, so Christmas is celebrated more widely. (Christians make up about 25-30% of the population.) However, the other 70% of people in South Korea are Buddhist (about 25%) or don't have a religion.
Unlike Japan, Christmas is an official public holiday - so some people have the day of work and school (although for some people it's just another working day or day at school)! But they go back on the 26th (Boxing Day). There's a longer official winter break in the New Year.
Churches are decorated with lights and many have a bright red neon cross on top (all the year!) so that goes very well with the Christmas lights! Most churches will have a service on Christmas day. Going to Church for Christmas is becoming more popular, even among non Christians.