West Des Moines is a city in Iowa, United States. Most of the city is in Polk County, some of it is in Dallas County, and small portions extend int…West Des Moines is a city in Iowa, United States. Most of the city is in Polk County, some of it is in Dallas County, and small portions extend into Warren and Madison Counties. As of the 2020 census, the city population was 68,723. West Des Moines is the third-most populous city in the Des Moines metropolitan area and the sixth-most populous city in Iowa.