Taejo of Goryeo
Once a part of the Lolang district of the Han Empire before the 4th century, this area was known as Ongcheon during the Three Kingdoms period. It was bestowed with the name in use today - Ongjin - during the reign of King Taejo of Goryeo, the founder of the Goryeo Dynasty. Then in 1018, during the 9th year of King Hyeonjong's reign over Goryeo, the county was established as one of the major administrative divisions in the heartland of the kingdom.