| | Affton, MO | Columbia, IL | United States |
| Population | 18,925 | 11,090 | 329,725,481 |
| Female Population | 49.0% | 50.0% | 50.5% |
| Male Population | 51.0% | 50.0% | 49.5% |
| Median Age | 42.5 | 39.3 | 38.4 |
| space3 | | | |
| Population - 2010 | 20,115 | 9,725 | 309,327,143 |
| Population - 2000 | 20,535 | 7,922 | 285,036,114 |
| Population - 1990 | 21,106 | 5,524 | 251,960,433 |
| Pop. 2000 to Now | 4.9% | 34.2% | 15.6% |
| Pop. 1990 to Now | 2.1% | 92.4% | 30.8% |
| space4 | | | |
| Population Density | 4,150.2 | 1,081.6 | 93.4 |
| Land Area | 4.6 | 10.3 | 3,531,905.4 |
| Water Area | 0.0 | 0.1 | 264,836.8 |
| space | | | |
| Est. Total Population By Age | | | |
| | Affton, MO | Columbia, IL | United States |
| Age 0 to 4 | 4.9% | 9.0% | 5.9% |
| Age 5 to 9 | 6.0% | 5.8% | 6.1% |
| Age 10 to 14 | 3.7% | 8.3% | 6.6% |
| Age 15 to 17 | 2.5% | 2.7% | 3.9% |
| Age 18 to 20 | 2.4% | 2.4% | 4.0% |
| Age 21 to 24 | 6.0% | 1.6% | 5.2% |
| Age 25 to 34 | 14.5% | 13.1% | 13.8% |
| Age 35 to 44 | 14.5% | 13.4% | 12.9% |
| Age 45 to 54 | 12.1% | 14.4% | 12.6% |
| Age 55 to 59 | 7.3% | 8.1% | 6.7% |
| Age 60 to 64 | 7.6% | 6.4% | 6.3% |
| Age 65 to 74 | 10.5% | 7.5% | 9.6% |
| Age 75 to 84 | 4.7% | 4.8% | 4.5% |
| Age 85 and over | 3.5% | 2.4% | 1.9% |
| space1 | | | |
| Race | | | |
| | Affton, MO | Columbia, IL | United States |
| White | 87.4% | 95.5% | 59.4% |
| Black | 2.8% | 0.1% | 12.2% |
| Asian | 2.3% | 1.0% | 5.6% |
| Native American | 0.1% | 0.0% | 0.6% |
| Hawaiian, Pacific Islander | 0.0% | 0.0% | 0.2% |
| Other | 0.0% | 0.7% | 0.4% |
| Two or More Races | 4.0% | 1.1% | 3.2% |
| Hispanic | 3.4% | 1.6% | 18.4% |
| space2 | | | |
| Marriage & Family | | | |
| | Affton, MO | Columbia, IL | United States |
| Married Population | 51.4% | 63.9% | 49.8% |
| Currently Married | 50.7% | 63.4% | 48.0% |
| Married but Separated | 0.7% | 0.5% | 1.8% |
| Single Population | 48.6% | 36.1% | 50.2% |
| Never Married | 29.3% | 21.8% | 33.8% |
| Divorced | 13.7% | 10.4% | 10.8% |
| Widowed | 5.6% | 3.9% | 5.6% |
| space5 | | | |
| Household Size | 2.20 | 2.60 | 2.60 |
| Households | 8,612 | 4,239 | 124,010,992 |
| Family Households | 4,837 | 3,102 | 80,755,759 |
| Married couple, w/children | 28.4% | 39.9% | 30.5% |
| Married couple, no children | 50.3% | 43.9% | 42.9% |
| Non Family Households | 3,775 | 1,137 | 43,255,233 |
| Single householder, w/children | 10.8% | 9.3% | 15.8% |
| Single householder, no children | 10.5% | 6.8% | 10.8% |