Arcadia is a city in Iron County, Missouri, United States. The population was 618 at the 2020 census. Arcadia was laid out and platted in 184…Arcadia is a city in Iron County, Missouri, United States. The population was 618 at the 2020 census. Arcadia was laid out and platted in 1849. It was named after the Greek region of Arcadia. A post office called Arcadia has been in operation since 1871.