 Onsong is the alleged site of the former Onsong concentration camp, now closed.Onsong was one of the six post/garrisons () established under the order of Sejong the Great of Joseon (1418–1450) to safeguard his people from the hostile Chinese and Manchurian nomads living in Manchuria.Onsong lies along the Tumen River, which forms the border with China.