|Area||14.48 sq mi (38 km2)|
|- land||14.35 sq mi (37 km2)|
|- water||0.12 sq mi (0 km2)|
|Mayor||Gary L. Graham|
|- summer (DST)||CDT (UTC-5)|
|Wikimedia Commons: O'Fallon, Illinois|
O'Fallon is a city in St. Clair County, Illinois, United States, and one of the fastest-growing communities in the Metropolitan St. Louis area. As of the 2010 census, the city had a total population of 28,281. The city is the third largest city in the Metro-East and Southern Illinois. Due to its close proximity to Scott Air Force Base, the population receives a boost from military and federal civilian personnel, defense contractors, and military retirees.
O'Fallon, along with its namesake in St. Charles County, Missouri is part of the St. Louis Metropolitan Statistical Area. This makes O'Fallon (along with the two Troys in Illinois and Missouri) one of the few pairs of like-named municipalities to be part of the same MSA.
|This section does not cite any references or sources. (March 2010)|
Founded in 1854, O'Fallon's namesake comes from Colonel John O'Fallon who was a wealthy gentleman from St. Louis. In downtown O'Fallon, a Baltimore and Ohio Railroad railroad depot was built, which helped put O'Fallon on the map. City lots were platted and sold at a public auction on May 18, 1854. A post office was established the following year and the city began attracting German settlers looking for fertile farming land. On January 27, 1874, O'Fallon was incorporated as a village. On March 14, 1905, the citizens voted for a change to the city form of government. Since its founding, O'Fallon has gained population every year except 1930, when the census showed a net loss of 23 people.
O'Fallon today 
Since the 1980s, growth in O'Fallon has accelerated. Following the expansion of Interstate 64, the 1990s saw a building boom with the construction of several now-established subdivisions including Thornbury Hills, Nolin Creek Estates, Fairwood Hills, Deer Creek, Forest Hills, and the completion of Fairwood East. O'Fallon Township High School's main campus at 600 South Smiley Street has undergone numerous additions over the past decades to ease overcrowding. A new city hall was completed in 1996. More than 50 percent of O'Fallon's housing is less than 15 years old.
Annual events 
- August – Homecoming
- September – Arts Festival
- November – Craft Fair
Parks and recreation 
- Family Sports Park
- Hesse Park
- Katy Cavin's Community Center
- O'Fallon Community Park
- O'Fallon Memorial Pool
- Rock Springs Nature Park
- Nature center
- Jogging/cycling paths
- Nature trails
- Natural prairie
- Dog Park
- St. Clair Recreation Complex
- St. Ellen Mine Park
- Thoman Park
- Veteran's Monument
- O'Fallon Public Library
Registered historic places 
- O'Fallon Community Consolidated School District # 90
- O'Fallon Central School District # 104
- O'Fallon District #203
- Private schools
O'Fallon is located at  O'Fallon is:(38.591549, −89.912000).
- 5 miles (8 km) from Scott Air Force Base
- 7 miles (11.5 km) from Lindenwood University – Belleville
- 10 miles (16 km) from McKendree University
- and 17 miles (27 km) from St. Louis, Missouri
According to the 2010 census, the city has a total area of 14.48 square miles (37.5 km2), of which 14.35 square miles (37.2 km2) (or 99.10%) is land and 0.12 square miles (0.31 km2) (or 0.83%) is water.
As of a special census of 2005, there are 25,647 people (up 3,737 from the census of 2000) and 10,468 households, with an average of 2 people per household. (down from 2.4 in 2000) The significant increase in population can be attributed to the ever-expanding suburbs of metropolitan St. Louis, Missouri and the influx of military personnel from nearby Scott Air Force Base.
The population density is 2,007.6 people per square mile (775.4/km²). There are 10,468 housing units at an average density of 790.4 per square mile (305.3/km²). The racial makeup of the city is 82.67% White, 11.99% African American, 0.23% Native American, 2.47% Asian, 0.07% Pacific Islander, 0.79% from other races, and 1.77% from two or more races. 2.23% of the population are Hispanic or Latino of any race.
There are 10,468 households out of which 39.6% have children under the age of 18 living with them, 59.0% are married couples living together, 10.5% have a female householder with no husband present, and 27.6% are non-families. 23.2% of all households are made up of individuals and 7.2% have someone living alone who is 65 years of age or older. The average household size is 2.62 and the average family size is 3.13.
In the city, the population is spread out with 28.3% under the age of 18, 8.0% from ages 18 to 24, 32.2% from ages 25 to 44, 22.7% from ages 45 to 64, and 8.9% who are age 65 or older. The median age is 35 years.
The median income for a household in the city is estimated at $68,534 and the median income for a family is $86,052. Males have a median income of $46,303 versus $30,158 for females. The per capita income for the city is $24,821. 5.0% of the population and 4.1% of families are below the poverty line. Out of the total population, 5.0% of those under the age of 18 and 7.9% of those 65 and older are living below the poverty line.
Notable people 
- Bob Cryder, professional football player
- Bernie Fuchs, illustrator
- William Holden, actor
- Dawn Stern, actress
Notable honors 
- The Official Site of Southwestern IL Police Consortium
- "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.
- Census Bureau
- "BillPullman.org". Retrieved 2013-2-3.
- The City of O'Fallon
- O'Fallon Historical Society
- O'Fallon Chamber of Commerce
- 360 Degree Panorama of the O'Fallon Veterans' Monument