Lewis is a city in Cass County, Iowa, United States, along the East Nishnabotna River. The population was 357 at the time of the 2020 c…Lewis is a city in Cass County, Iowa, United States, along the East Nishnabotna River. The population was 357 at the time of the 2020 census. Lewis is located at 41°18′19″N 95°5′4″W / 41.30528°N 95.08444°W.