Langdon is a city in Cavalier County, North Dakota, United States. It is the county seat of Cavalier County. The population was 1,878 at the 2010 census. Langdon was designated as the county seat in 1884 and was incorporated in 1885.
A post office has been in operation in Langdon since 1886. The city was named for Robert Bruce Langdon, a politician and railroad official.
On Memorial Day (then called Decoration Day) 1909, a tornado struck on the prairie a mile to a mile and a half southeast of Langdon, then moved seven miles in a northwest direction. The tornado, locally dubbed The Vulcan, killed five people and injured 29. Notably, Mrs. M.L. Sullivan ran for safety but the tornado hit as she arrived at her cellar door. When the winds subsided, she was standing in the cellar with its broken doorknob in her hand.