Usi is a kun, or county, in westernmost Chagang province, North Korea. It looks across the Yalu River into the People's Republic of China. Within North Korea, it borers Chosan and Kopung to the east, Songwon to the south, and North Pyongan's Pyoktong county to the west. Originally part of Pyoktong, it was made a separate county in 1952 as part of a general reorganization of local government; in 1954, it was transferred from North Pyongan to Chagang.