Johnson County Courthouse, downtown
|Area||2.88 sq mi (7 km2)|
|- land||2.84 sq mi (7 km2)|
|- water||0.04 sq mi (0 km2)|
|Density||550.8 / sq mi (213 / km2)|
|- summer (DST)||CDT (UTC-5)|
|Wikimedia Commons: Vienna, Illinois|
- For the Illinois village formerly known as Vienna, see Astoria, Illinois
Vienna i// 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. The Trail of Tears halfway point commemorative totem and flags are located in the adjacent city park. The town's name is pronounced differently, by most people, from the English name for the Austrian capital of the same name.
Vienna is located at (37.416103, -88.894268).
According to the 2010 census, the city has a total area of 2.88 square miles (7.5 km2), of which 2.84 square miles (7.4 km2) (or 98.61%) is land and 0.04 square miles (0.10 km2) (or 1.39%) is water.
As of the census of 2000, there were 1,234 people, 560 households, and 309 families residing in the city. The population density was 550.8 people per square mile (212.7/km²). There were 607 housing units at an average density of 270.9 per square mile (104.6/km²). The racial makeup of the city was 97.89% White, 0.08% African American, 0.08% Asian, 0.81% from other races, and 1.13% from two or more races. Hispanic or Latino of any race were 1.94% of the population.
There were 560 households out of which 27.7% had children under the age of 18 living with them, 39.5% were married couples living together, 13.2% had a female householder with no husband present, and 44.8% were non-families. 41.4% of all households were made up of individuals and 25.5% had someone living alone who was 65 years of age or older. The average household size was 2.12 and the average family size was 2.89.
In the city the population was spread out with 22.6% under the age of 18, 9.0% from 18 to 24, 23.8% from 25 to 44, 18.3% from 45 to 64, and 26.3% who were 65 years of age or older. The median age was 40 years. For every 100 females there were 77.0 males. For every 100 females age 18 and over, there were 70.8 males.
The median income for a household in the city was $21,702, and the median income for a family was $31,250. Males had a median income of $34,583 versus $17,614 for females. The per capita income for the city was $13,662. About 17.7% of families and 20.0% of the population were below the poverty line, including 27.0% of those under age 18 and 21.4% of those age 65 or over.
Notable people 
- Pleasant T. Chapman, congressman, born nearby and practiced law here
- George W. English, United States District Court judge, born nearby, practiced law here, was impeached in 1926
- William Heirens, reputed serial-killer, spent 23 years at the Vienna Correctional Center
- Andrew J. Kuykendall, congressman, practiced law here
- Paul Powell, former Illinois Secretary of State, born here
- "Find a County". National Association of Counties. Retrieved 2011-06-07.
- "US Gazetteer files: 2010, 2000, and 1990". United States Census Bureau. 2011-02-12. Retrieved 2011-04-23.
- "2010 Census U.S. Gazetteer Files for Places – Illinois". United States Census. Retrieved 2012-10-13.
- "American FactFinder". United States Census Bureau. Retrieved 2008-01-31.