Changjin County is a mountainous county in South Hamgyong province, North Korea. Changjin lies on the Rangrim and Pujonryong ranges, and most of the county sits atop the Kaema Plateau. Due to this location, Changjin has a particularly cold climate. The highest point is Ryonhwasan (련화산). The chief stream is the Changjin River. Lake Changjin is a large reservoir in Changjin County.