There are 5 US Post Offices in Cavalier County serving a total of 3,495 residents equating to 699 residents per post office. It's estimated that approximately 5,578 packages are handled across the 5 county post offices annually. Cavalier County is a county located in the U.S. state of North Dakota. As of the 2010 Census, the population was 3,993. Its county seat is Langdon. The county was created by the 1873 territorial legislature and named for Charles Cavileer of Pembina (1818\u20131902), one of the earliest white settlers. The county was organized on July 8, 1884. It is south of the Canada\u2013US border with Manitoba. The city of Cavalier is actually in nearby Pembina County."