Vienna is a city in Johnson County, Illinois, United States. It is the county seat of Johnson County, and the site of two well-known state penitentiaries. Heron Pond - Little Black Slough Nature Preserve, a National Natural Landmark, is nearby. The Tunnel Hill State Trail trail-head and headquarters is located in Vienna. The Trail of Tears halfway point commemorative totem and flags are located in the adjacent city park. According to the United States Census Bureau, the city has a total area of 2.2 square miles (5.7km2), of which, 2.2 square miles (5.7km2) of it is land and 0.44% is water.