Within North Korea, it borders Chosan and Kopung to the east, Songwon to the south, and North Pyongan Province'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.

The stretch of the Yalu in Usi is part of the massive "Lake Supung", North Korea's largest reservoir.

The Yalu valley is farmed for rice, while the upland regions produce maize, potatoes, and sesame.

Usi county is divided into one town (ŭp), one worker's district (rodongjagu), and 22 villages (ri).