Minnehaha County is a county on the eastern border of the state of South Dakota. As of the 2020 census, the population was 197,214, making it the state's most populous county. It contains over 20% of the state's population. Its county seat is Sioux Falls, South Dakota's most populous city. The county was created in 1862 and organized in 1868. Its name was derived from the Sioux word Mnihaha, meaning "rapid water," or "waterfall".

Sioux Falls is the most populous city in the U.S. state of South Dakota and the 121st-most populous city in the United States. It is the county seat of Minnehaha County and also extends into northern Lincoln County to the south, which continues up to the Iowa state line. The population was 192,517 at the 2020 census, and in 2022, its estimated population was 202,078. According to city officials, the estimated population had grown to 213,891 as of early 2024. The Sioux Falls metro area accounts for more than 30% of the state's population. Chartered in 1856 on the banks of the Big Sioux River, the city is situated in the rolling hills at the junction of interstates 29 and 90.