Cavalier County is a county in the U.S. state of North Dakota. It is south of the Canada–US border with Manitoba. As of the 2020 census, the population was 3,704. Its county seat is Langdon. The city of Cavalier is in nearby Pembina County.

Langdon is a city in Cavalier County, North Dakota, United States. It is the county seat of Cavalier County. The population was 1,909 at the 2020 census. Langdon was designated as the county seat in 1884 and was incorporated in 1885.