Southwest City is a city in McDonald County, Missouri, United States. The population was 922 at the 2020 census. It is located in the southwest…Southwest City is a city in McDonald County, Missouri, United States. The population was 922 at the 2020 census. It is located in the southwestern corner of the state of Missouri. Southwest City was platted in 1870. It was named from its location in the southwest corner of the county and state.