De Soto is a city in Dallas County, Iowa, United States. The population was 915 at the time of the 2020 census. It is part of the Des Moines–…De Soto is a city in Dallas County, Iowa, United States. The population was 915 at the time of the 2020 census. It is part of the Des Moines–West Des Moines Metropolitan Statistical Area. De Soto got its start in the year 1868, following construction of the Chicago, Rock Island and Pacific Railroad through the territory. De Soto is the name of a railroad official.