For the Illinois village formerly known as Vienna, see Astoria, Illinois Vienna Listen/vaɪˈænə/ is a city in Johnson County, Illinois, United States. The population was 1,434 at the 2010 census. 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.