Kosŏng is a county located in Kangwŏn province in North Korea. It occupies the southeasternmost corner of the country and is situated immediately north of the Korean Demilitarized Zone.
Historically, prior to the conclusion of the Korean War in 1953, Kosŏng existed as a single county that now encompasses territory in both North and South Korea. Following a subsequent reorganization, the current North Korean county absorbed the southern portion of Tongch'ŏn county.