South Korea has a long history of religious observance. Buddhism was introduced in 372 and currently has nearly 11 million adherents worshiping in tens of thousands of temples. Confucianism became the state ideology during the Joseon Dynasty which lasted from 1392 to 1910 but while listed as a religion, is more of an ethical way of thinking and living (but has had profound influence on Korean society).
Roman Catholicism came to Korea in the late 18th century following the baptism of one of the “elite” on a visit to China. Catholics faced significant persecution during the Joseon Dynasty (making Korea the 4th largest contributor of saints) but grew rapidly following the end of the Korean War and now claims over 5 million members.
Protestant Christianity came to Korea with Christian missionaries from North America in the late 19th century. Much of the appeal of the Protestant Church in Korea came from significant investment in schools and hospitals. Today, Protestants comprise about 18% of the population of South Korea, nearly 9 million members.
Combining members of Protestantism and Catholicism nets a total of nearly 15 million members or over half of the population claiming religious adherence, making Christianity the largest faith group in South Korea.

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A short trip through nearly any part of Korea will reveal evidence of South Korea’s religious nature. Driving through most any town you’ll often see a steeple or gold Buddha. Here are a few pictures of some of the churches and temples I have seen in my travels:
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The religious preference chart and some of the information in this post came from http://www.korea.net/AboutKorea/Korean-Life/Religion.
Some other information came from http://www.aljazeera.com/indepth/opinion/2014/08/why-catholicism-important-korea-201481717037383818.html.
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