Soldier is a city in Monona County, Iowa, United States, along the Soldier River. The population was 184 at the time of the 2020 census. Soldieā¦Soldier is a city in Monona County, Iowa, United States, along the Soldier River. The population was 184 at the time of the 2020 census. Soldier was so named from a nearby unmarked grave of a soldier.