Mount Vernon is a city in Davison County, South Dakota, United States. The population was 461 at the 2020 census. It is part of the Mitchell, South Dakota Micropolitan Statistical Area.

Davison County is a county in the U.S. state of South Dakota. As of the 2020 census, the population was 19,956, making it the 10th most populous county in South Dakota. Its county seat is Mitchell. The county was created in 1873 and organized in 1874. It was named for Henry C. Davison, the first settler in the county.