| | Athens, OH | Belvidere, IL | United States |
| Population | 24,507 | 25,179 | 329,725,481 |
| Female Population | 51.7% | 52.3% | 50.5% |
| Male Population | 48.3% | 47.7% | 49.5% |
| Median Age | 21.6 | 36.9 | 38.4 |
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| Population - 2010 | 24,253 | 25,598 | 309,327,143 |
| Population - 2000 | 21,342 | 20,820 | 285,036,114 |
| Population - 1990 | 21,265 | 15,958 | 251,960,433 |
| Pop. 2000 to Now | 15.3% | 18.8% | 15.6% |
| Pop. 1990 to Now | 15.7% | 55.0% | 30.8% |
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| Population Density | 2,493.8 | 2,085.9 | 93.4 |
| Land Area | 9.8 | 12.1 | 3,531,905.4 |
| Water Area | 0.2 | 0.2 | 264,836.8 |
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| Est. Total Population By Age | | | |
| | Athens, OH | Belvidere, IL | United States |
| Age 0 to 4 | 1.9% | 5.9% | 5.9% |
| Age 5 to 9 | 2.0% | 7.1% | 6.1% |
| Age 10 to 14 | 2.0% | 7.2% | 6.6% |
| Age 15 to 17 | 1.7% | 3.6% | 3.9% |
| Age 18 to 20 | 35.0% | 4.5% | 4.0% |
| Age 21 to 24 | 24.7% | 4.5% | 5.2% |
| Age 25 to 34 | 12.3% | 13.4% | 13.8% |
| Age 35 to 44 | 5.6% | 11.9% | 12.9% |
| Age 45 to 54 | 4.2% | 13.5% | 12.6% |
| Age 55 to 59 | 3.0% | 7.5% | 6.7% |
| Age 60 to 64 | 2.3% | 4.8% | 6.3% |
| Age 65 to 74 | 3.4% | 10.1% | 9.6% |
| Age 75 to 84 | 0.9% | 4.4% | 4.5% |
| Age 85 and over | 0.8% | 1.4% | 1.9% |
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| Race | | | |
| | Athens, OH | Belvidere, IL | United States |
| White | 82.2% | 60.1% | 59.4% |
| Black | 4.5% | 1.3% | 12.2% |
| Asian | 5.6% | 0.9% | 5.6% |
| Native American | 0.2% | 0.0% | 0.6% |
| Hawaiian, Pacific Islander | 0.2% | 0.0% | 0.2% |
| Other | 0.1% | 0.2% | 0.4% |
| Two or More Races | 3.9% | 1.1% | 3.2% |
| Hispanic | 3.3% | 36.4% | 18.4% |
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| Marriage & Family | | | |
| | Athens, OH | Belvidere, IL | United States |
| Married Population | 16.5% | 42.0% | 49.8% |
| Currently Married | 15.8% | 39.9% | 48.0% |
| Married but Separated | 0.7% | 2.1% | 1.8% |
| Single Population | 83.6% | 58.0% | 50.2% |
| Never Married | 78.8% | 36.6% | 33.8% |
| Divorced | 3.5% | 14.5% | 10.8% |
| Widowed | 1.3% | 6.9% | 5.6% |
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| Household Size | 2.46 | 2.71 | 2.60 |
| Households | 6,750 | 9,193 | 124,010,992 |
| Family Households | 2,172 | 5,829 | 80,755,759 |
| Married couple, w/children | 34.0% | 26.5% | 30.5% |
| Married couple, no children | 42.3% | 37.6% | 42.9% |
| Non Family Households | 4,578 | 3,364 | 43,255,233 |
| Single householder, w/children | 10.5% | 23.0% | 15.8% |
| Single householder, no children | 13.2% | 12.9% | 10.8% |