Langdon is a city in Reno County, Kansas, United States. As of the 2020 census, the population of the city was 39. The first post office in Lang…Langdon is a city in Reno County, Kansas, United States. As of the 2020 census, the population of the city was 39. The first post office in Langdon was established in 1873. Langdon was named for a local businessman.