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. Since the 1980s, growth in O'Fallon has accelerated. With the expansion of Interstate 64, O'Fallon has increasingly become an important commercial and residential satellite of St. Louis' suburban orbit. Despite the recent housing market bust, the Metro East has been relatively resilient, as housing starts are still well above the national average.
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/sq mi (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 $55,927, and the median income for a family is $66,262. 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.
