| | Oak Forest, IL | Grayslake, IL | United States |
| Population | 27,445 | 20,827 | 329,725,481 |
| Female Population | 49.7% | 48.9% | 50.5% |
| Male Population | 50.3% | 51.1% | 49.5% |
| Median Age | 41.1 | 37.7 | 38.4 |
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| Population - 2010 | 28,022 | 21,064 | 309,327,143 |
| Population - 2000 | 28,051 | 18,506 | 285,036,114 |
| Population - 1990 | 26,203 | 7,388 | 251,960,433 |
| Pop. 2000 to Now | -4.2% | 11.2% | 15.6% |
| Pop. 1990 to Now | 2.6% | 178.6% | 30.8% |
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| Population Density | 4,576.5 | 1,896.0 | 93.4 |
| Land Area | 6.0 | 11.0 | 3,531,905.4 |
| Water Area | 0.0 | 0.2 | 264,836.8 |
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| Est. Total Population By Age | | | |
| | Oak Forest, IL | Grayslake, IL | United States |
| Age 0 to 4 | 3.7% | 6.7% | 5.9% |
| Age 5 to 9 | 6.2% | 5.9% | 6.1% |
| Age 10 to 14 | 7.2% | 6.4% | 6.6% |
| Age 15 to 17 | 4.3% | 4.3% | 3.9% |
| Age 18 to 20 | 3.4% | 3.5% | 4.0% |
| Age 21 to 24 | 5.4% | 6.0% | 5.2% |
| Age 25 to 34 | 12.1% | 13.2% | 13.8% |
| Age 35 to 44 | 12.5% | 13.2% | 12.9% |
| Age 45 to 54 | 14.8% | 15.0% | 12.6% |
| Age 55 to 59 | 8.6% | 7.7% | 6.7% |
| Age 60 to 64 | 6.6% | 6.1% | 6.3% |
| Age 65 to 74 | 9.8% | 7.6% | 9.6% |
| Age 75 to 84 | 4.7% | 3.3% | 4.5% |
| Age 85 and over | 0.8% | 1.2% | 1.9% |
| space1 | | | |
| Race | | | |
| | Oak Forest, IL | Grayslake, IL | United States |
| White | 69.0% | 72.0% | 59.4% |
| Black | 6.2% | 6.9% | 12.2% |
| Asian | 6.3% | 5.9% | 5.6% |
| Native American | 0.1% | 0.1% | 0.6% |
| Hawaiian, Pacific Islander | 0.0% | 0.3% | 0.2% |
| Other | 0.4% | 0.6% | 0.4% |
| Two or More Races | 2.1% | 4.4% | 3.2% |
| Hispanic | 16.0% | 9.8% | 18.4% |
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| Marriage & Family | | | |
| | Oak Forest, IL | Grayslake, IL | United States |
| Married Population | 57.0% | 57.8% | 49.8% |
| Currently Married | 56.5% | 56.7% | 48.0% |
| Married but Separated | 0.4% | 1.1% | 1.8% |
| Single Population | 43.0% | 42.2% | 50.2% |
| Never Married | 30.5% | 30.4% | 33.8% |
| Divorced | 8.4% | 8.4% | 10.8% |
| Widowed | 4.2% | 3.4% | 5.6% |
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| Household Size | 2.67 | 2.65 | 2.60 |
| Households | 10,261 | 7,817 | 124,010,992 |
| Family Households | 7,298 | 5,432 | 80,755,759 |
| Married couple, w/children | 28.5% | 41.1% | 30.5% |
| Married couple, no children | 52.1% | 44.5% | 42.9% |
| Non Family Households | 2,963 | 2,385 | 43,255,233 |
| Single householder, w/children | 12.3% | 7.4% | 15.8% |
| Single householder, no children | 7.1% | 7.0% | 10.8% |