Dearborn is a city in Buchanan and Platte counties in the U.S. state of Missouri and is part of the Kansas City metropolitan area. The popula…Dearborn is a city in Buchanan and Platte counties in the U.S. state of Missouri and is part of the Kansas City metropolitan area. The population was 482 at the 2020 census. The city was named for Henry Dearborn, Revolutionary War general and Secretary of War, and was incorporated in 1882.