Cavalier county is located in northeastern North Dakota on the Canadian border one county removed from the Red River of the North with Langdon as its county seat. The county population on July 1, 1999, was 4,821, a decrease of 1,243 over the 1990 census.

Natural features include Rush Lake, in the northwestern section of the county; the main and south forks of the Pembina River, to the north and east and short sections of the Park and Tongue rivers.