| | Forest Park, IL | DeKalb, IL | United States |
| Population | 14,297 | 41,083 | 329,725,481 |
| Female Population | 53.1% | 50.4% | 50.5% |
| Male Population | 46.9% | 49.6% | 49.5% |
| Median Age | 42.4 | 25.1 | 38.4 |
| space3 | | | |
| Population - 2010 | 14,174 | 44,107 | 309,327,143 |
| Population - 2000 | 15,688 | 39,018 | 285,036,114 |
| Population - 1990 | 14,918 | 34,925 | 251,960,433 |
| Pop. 2000 to Now | -13.7% | 9.2% | 15.6% |
| Pop. 1990 to Now | -9.3% | 22.0% | 30.8% |
| space4 | | | |
| Population Density | 5,952.1 | 2,545.6 | 93.4 |
| Land Area | 2.4 | 16.1 | 3,531,905.4 |
| Water Area | 0.0 | 0.2 | 264,836.8 |
| space | | | |
| Est. Total Population By Age | | | |
| | Forest Park, IL | DeKalb, IL | United States |
| Age 0 to 4 | 5.1% | 5.1% | 5.9% |
| Age 5 to 9 | 2.7% | 5.2% | 6.1% |
| Age 10 to 14 | 4.4% | 5.6% | 6.6% |
| Age 15 to 17 | 2.3% | 3.1% | 3.9% |
| Age 18 to 20 | 1.4% | 13.0% | 4.0% |
| Age 21 to 24 | 5.6% | 17.9% | 5.2% |
| Age 25 to 34 | 16.8% | 14.5% | 13.8% |
| Age 35 to 44 | 15.8% | 9.4% | 12.9% |
| Age 45 to 54 | 13.0% | 8.2% | 12.6% |
| Age 55 to 59 | 8.7% | 4.9% | 6.7% |
| Age 60 to 64 | 6.6% | 3.5% | 6.3% |
| Age 65 to 74 | 12.5% | 5.5% | 9.6% |
| Age 75 to 84 | 3.7% | 2.4% | 4.5% |
| Age 85 and over | 1.4% | 1.8% | 1.9% |
| space1 | | | |
| Race | | | |
| | Forest Park, IL | DeKalb, IL | United States |
| White | 54.2% | 60.5% | 59.4% |
| Black | 27.9% | 14.5% | 12.2% |
| Asian | 5.1% | 4.0% | 5.6% |
| Native American | 0.1% | 0.1% | 0.6% |
| Hawaiian, Pacific Islander | 0.0% | 0.0% | 0.2% |
| Other | 1.0% | 0.2% | 0.4% |
| Two or More Races | 4.0% | 4.6% | 3.2% |
| Hispanic | 7.7% | 16.1% | 18.4% |
| space2 | | | |
| Marriage & Family | | | |
| | Forest Park, IL | DeKalb, IL | United States |
| Married Population | 36.4% | 30.8% | 49.8% |
| Currently Married | 33.2% | 30.1% | 48.0% |
| Married but Separated | 3.2% | 0.8% | 1.8% |
| Single Population | 63.6% | 69.2% | 50.2% |
| Never Married | 43.7% | 58.0% | 33.8% |
| Divorced | 14.7% | 7.2% | 10.8% |
| Widowed | 5.2% | 4.0% | 5.6% |
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| Household Size | 2.02 | 2.35 | 2.60 |
| Households | 6,961 | 15,867 | 124,010,992 |
| Family Households | 3,248 | 7,826 | 80,755,759 |
| Married couple, w/children | 17.8% | 26.7% | 30.5% |
| Married couple, no children | 41.9% | 35.8% | 42.9% |
| Non Family Households | 3,713 | 8,041 | 43,255,233 |
| Single householder, w/children | 22.5% | 25.3% | 15.8% |
| Single householder, no children | 17.8% | 12.3% | 10.8% |