Changjin lies on the Rangrim and Pujŏllyong ranges, and most of the county sits atop the Kaema Plateau.

Changjin County is divided into 1 ŭp (town), 3 rodongjagu (workers' districts) and 16 ri (villages): In historical contexts the lake is sometimes known according to its Japanese pronunciation, as the Chōshin Reservoir.

[3] (but most likely the Japanese pronunciation of the Korean name, for the actual Kanji; 長津湖, is read out as Nagatsu mizuumi) read out asIn 1950 it was the site of a major battle of the Korean War, the Battle of Chosin Reservoir, in which the Chinese People's Volunteer Army stopped the northward advance of the United Nations allied forces, but paid a heavy price in casualties.

Changjin produces large amounts of lumber, and leads the province in mine production.

Deposits of silver, graphite, jade, and gold are found in the area.