O'Fallon, Illinois, is classified as a "White Majority" city with moderate diversity. As of 2022, the white population comprises 68% of the total, while Black (15%) and Hispanic (6%) communities have significant representation. The city's population has grown steadily, reaching 35,662 residents in 2022. O'Fallon is relatively affluent, with a median household income of $100,126 in 2022, above the national average.

O'Fallon has been transitioning from a "Low Diversity" community towards a more diverse demographic makeup over the past decade. In 2013, 76% of the population identified as white. By 2022, this percentage had decreased to 68%, indicating a gradual but consistent shift towards greater diversity. The Black population has remained relatively stable, fluctuating between 12-16% over the decade. The Hispanic community has grown from 3% in 2013 to 6% in 2022, and those identifying as two or more races have increased from 3% to 7% in the same period.

The city's economic landscape has improved alongside its increasing diversity. Median household income has grown from $95,499 in 2013 to $100,126 in 2022, representing a 4.8% increase. This growth outpaces inflation for much of this period, indicating real economic gains for residents. The population has grown steadily, from 32,878 in 2013 to 35,662 in 2022, a 8.5% increase. This population growth, coupled with rising incomes, suggests that O'Fallon has remained an attractive destination for diverse groups of people.