Mapleton is a city in Monona County, Iowa, United States. The population was 1,165 at the time of the 2020 census. Mapleton was platted in 18…Mapleton is a city in Monona County, Iowa, United States. The population was 1,165 at the time of the 2020 census. Mapleton was platted in 1857 when the railroad was extended to that point. It was named from its location near the Maple River.