| | Frankfort Square, IL | St. John, IN | United States |
| Population | 9,214 | 19,805 | 329,725,481 |
| Female Population | 51.0% | 50.7% | 50.5% |
| Male Population | 49.0% | 49.3% | 49.5% |
| Median Age | 40.1 | 41.9 | 38.4 |
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| Population - 2010 | 9,525 | 14,873 | 309,327,143 |
| Population - 2000 | 7,766 | 8,382 | 285,036,114 |
| Population - 1990 | 6,227 | 4,921 | 251,960,433 |
| Pop. 2000 to Now | 19.0% | 134.0% | 15.6% |
| Pop. 1990 to Now | 48.5% | 298.6% | 30.8% |
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| Population Density | 3,611.9 | 1,577.7 | 93.4 |
| Land Area | 2.6 | 12.6 | 3,531,905.4 |
| Water Area | 0.0 | 0.1 | 264,836.8 |
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| Est. Total Population By Age | | | |
| | Frankfort Square, IL | St. John, IN | United States |
| Age 0 to 4 | 3.6% | 5.7% | 5.9% |
| Age 5 to 9 | 5.2% | 5.3% | 6.1% |
| Age 10 to 14 | 8.9% | 9.2% | 6.6% |
| Age 15 to 17 | 6.7% | 4.8% | 3.9% |
| Age 18 to 20 | 4.6% | 3.7% | 4.0% |
| Age 21 to 24 | 5.5% | 4.2% | 5.2% |
| Age 25 to 34 | 9.8% | 7.3% | 13.8% |
| Age 35 to 44 | 12.8% | 13.7% | 12.9% |
| Age 45 to 54 | 17.9% | 15.8% | 12.6% |
| Age 55 to 59 | 7.8% | 6.0% | 6.7% |
| Age 60 to 64 | 6.8% | 7.9% | 6.3% |
| Age 65 to 74 | 8.6% | 10.1% | 9.6% |
| Age 75 to 84 | 1.4% | 5.1% | 4.5% |
| Age 85 and over | 0.5% | 1.1% | 1.9% |
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| Race | | | |
| | Frankfort Square, IL | St. John, IN | United States |
| White | 79.6% | 79.2% | 59.4% |
| Black | 5.2% | 2.6% | 12.2% |
| Asian | 0.7% | 2.2% | 5.6% |
| Native American | 0.0% | 0.2% | 0.6% |
| Hawaiian, Pacific Islander | 0.0% | 0.1% | 0.2% |
| Other | 0.2% | 2.3% | 0.4% |
| Two or More Races | 7.2% | 2.3% | 3.2% |
| Hispanic | 7.1% | 11.1% | 18.4% |
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| Marriage & Family | | | |
| | Frankfort Square, IL | St. John, IN | United States |
| Married Population | 60.5% | 66.0% | 49.8% |
| Currently Married | 59.9% | 65.4% | 48.0% |
| Married but Separated | 0.6% | 0.5% | 1.8% |
| Single Population | 39.5% | 34.0% | 50.2% |
| Never Married | 30.2% | 24.1% | 33.8% |
| Divorced | 8.0% | 5.3% | 10.8% |
| Widowed | 1.3% | 4.6% | 5.6% |
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| Household Size | 2.95 | 2.87 | 2.60 |
| Households | 3,124 | 6,905 | 124,010,992 |
| Family Households | 2,788 | 5,629 | 80,755,759 |
| Married couple, w/children | 35.8% | 43.3% | 30.5% |
| Married couple, no children | 43.1% | 46.5% | 42.9% |
| Non Family Households | 336 | 1,276 | 43,255,233 |
| Single householder, w/children | 13.2% | 5.6% | 15.8% |
| Single householder, no children | 7.9% | 4.6% | 10.8% |