Mondamin is a city in Harrison County, Iowa, United States. The population was 339 at the time of the 2020 census. Mondamin was pl…Mondamin is a city in Harrison County, Iowa, United States. The population was 339 at the time of the 2020 census. Mondamin was platted in the winter of 1867–1868 when the railroad was extended to that point. It was named after Mondamin, a Native American corn deity.