| | Marion, IN | Warren, OH | United States |
| Population | 27,757 | 39,334 | 329,725,481 |
| Female Population | 54.0% | 51.4% | 50.5% |
| Male Population | 46.0% | 48.6% | 49.5% |
| Median Age | 36.6 | 40.2 | 38.4 |
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| Population - 2010 | 29,824 | 41,480 | 309,327,143 |
| Population - 2000 | 31,320 | 46,832 | 285,036,114 |
| Population - 1990 | 32,618 | 50,793 | 251,960,433 |
| Pop. 2000 to Now | -11.6% | -17.8% | 15.6% |
| Pop. 1990 to Now | -15.2% | -24.2% | 30.8% |
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| Population Density | 1,781.0 | 2,463.3 | 93.4 |
| Land Area | 15.6 | 16.0 | 3,531,905.4 |
| Water Area | 0.1 | 0.2 | 264,836.8 |
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| Est. Total Population By Age | | | |
| | Marion, IN | Warren, OH | United States |
| Age 0 to 4 | 5.1% | 5.8% | 5.9% |
| Age 5 to 9 | 4.5% | 5.3% | 6.1% |
| Age 10 to 14 | 6.5% | 6.3% | 6.6% |
| Age 15 to 17 | 2.9% | 3.4% | 3.9% |
| Age 18 to 20 | 8.9% | 3.5% | 4.0% |
| Age 21 to 24 | 9.4% | 6.3% | 5.2% |
| Age 25 to 34 | 11.6% | 13.9% | 13.8% |
| Age 35 to 44 | 8.4% | 11.6% | 12.9% |
| Age 45 to 54 | 10.0% | 12.0% | 12.6% |
| Age 55 to 59 | 6.9% | 6.6% | 6.7% |
| Age 60 to 64 | 6.8% | 7.9% | 6.3% |
| Age 65 to 74 | 10.5% | 9.4% | 9.6% |
| Age 75 to 84 | 5.6% | 5.3% | 4.5% |
| Age 85 and over | 2.9% | 2.6% | 1.9% |
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| Race | | | |
| | Marion, IN | Warren, OH | United States |
| White | 73.0% | 63.6% | 59.4% |
| Black | 13.9% | 26.5% | 12.2% |
| Asian | 1.1% | 0.9% | 5.6% |
| Native American | 0.3% | 0.1% | 0.6% |
| Hawaiian, Pacific Islander | 0.0% | 0.0% | 0.2% |
| Other | 0.1% | 0.3% | 0.4% |
| Two or More Races | 4.7% | 5.0% | 3.2% |
| Hispanic | 7.0% | 3.6% | 18.4% |
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| Marriage & Family | | | |
| | Marion, IN | Warren, OH | United States |
| Married Population | 31.7% | 31.8% | 49.8% |
| Currently Married | 30.6% | 28.4% | 48.0% |
| Married but Separated | 1.1% | 3.4% | 1.8% |
| Single Population | 68.3% | 68.2% | 50.2% |
| Never Married | 41.1% | 42.4% | 33.8% |
| Divorced | 19.5% | 17.9% | 10.8% |
| Widowed | 7.6% | 7.9% | 5.6% |
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| Household Size | 2.18 | 2.19 | 2.60 |
| Households | 10,806 | 16,817 | 124,010,992 |
| Family Households | 5,848 | 8,563 | 80,755,759 |
| Married couple, w/children | 19.6% | 15.5% | 30.5% |
| Married couple, no children | 36.9% | 33.2% | 42.9% |
| Non Family Households | 4,958 | 8,254 | 43,255,233 |
| Single householder, w/children | 30.3% | 31.1% | 15.8% |
| Single householder, no children | 13.2% | 20.2% | 10.8% |