Lennox is a city in Lincoln County, South Dakota, United States, located 20 miles southwest of Sioux Falls. The population was 2,423 at the 2…Lennox is a city in Lincoln County, South Dakota, United States, located 20 miles southwest of Sioux Falls. The population was 2,423 at the 2020 census. The city has the name of Ben Lennox, private secretary to the general manager to the Milwaukee Railroad.