 According to the United States Census Bureau, the city has a total area of 17.7 square miles (45.9 km²), of which 17.7 square miles (45.9 km²) is land and 0.04 square mile (0.1 km²) (0.17%) is water.The official main street of Spring Hill is also called US Highway 31, Columbia Pike or Nashville Highway.As of the 2010 United States Census, there were 29,036 people, 9,861 households, and 7,884 families living in the city.