| | St. Joseph, MI | Merrillville, IN | United States |
| Population | 7,868 | 36,196 | 329,725,481 |
| Female Population | 50.7% | 52.0% | 50.5% |
| Male Population | 49.3% | 48.0% | 49.5% |
| Median Age | 42.9 | 38.7 | 38.4 |
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| Population - 2010 | 8,358 | 34,960 | 309,327,143 |
| Population - 2000 | 8,789 | 30,560 | 285,036,114 |
| Population - 1990 | 9,214 | 27,257 | 251,960,433 |
| Pop. 2000 to Now | -5.7% | 14.3% | 15.6% |
| Pop. 1990 to Now | -10.0% | 28.1% | 30.8% |
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| Population Density | 2,456.5 | 1,089.9 | 93.4 |
| Land Area | 3.2 | 33.2 | 3,531,905.4 |
| Water Area | 1.6 | 0.0 | 264,836.8 |
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| Est. Total Population By Age | | | |
| | St. Joseph, MI | Merrillville, IN | United States |
| Age 0 to 4 | 4.6% | 4.8% | 5.9% |
| Age 5 to 9 | 3.8% | 7.6% | 6.1% |
| Age 10 to 14 | 4.5% | 6.5% | 6.6% |
| Age 15 to 17 | 2.2% | 5.1% | 3.9% |
| Age 18 to 20 | 2.4% | 3.4% | 4.0% |
| Age 21 to 24 | 5.9% | 5.9% | 5.2% |
| Age 25 to 34 | 14.7% | 11.8% | 13.8% |
| Age 35 to 44 | 13.7% | 12.5% | 12.9% |
| Age 45 to 54 | 12.3% | 11.4% | 12.6% |
| Age 55 to 59 | 6.6% | 6.6% | 6.7% |
| Age 60 to 64 | 7.2% | 6.2% | 6.3% |
| Age 65 to 74 | 12.5% | 10.7% | 9.6% |
| Age 75 to 84 | 4.8% | 5.3% | 4.5% |
| Age 85 and over | 4.9% | 2.2% | 1.9% |
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| Race | | | |
| | St. Joseph, MI | Merrillville, IN | United States |
| White | 84.3% | 34.6% | 59.4% |
| Black | 4.6% | 44.9% | 12.2% |
| Asian | 3.8% | 1.3% | 5.6% |
| Native American | 1.6% | 0.1% | 0.6% |
| Hawaiian, Pacific Islander | 0.0% | 0.0% | 0.2% |
| Other | 0.2% | 0.3% | 0.4% |
| Two or More Races | 3.0% | 3.0% | 3.2% |
| Hispanic | 2.5% | 15.9% | 18.4% |
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| Marriage & Family | | | |
| | St. Joseph, MI | Merrillville, IN | United States |
| Married Population | 50.8% | 39.7% | 49.8% |
| Currently Married | 50.2% | 37.6% | 48.0% |
| Married but Separated | 0.6% | 2.1% | 1.8% |
| Single Population | 49.2% | 60.3% | 50.2% |
| Never Married | 30.7% | 39.7% | 33.8% |
| Divorced | 13.1% | 13.0% | 10.8% |
| Widowed | 5.4% | 7.6% | 5.6% |
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| Household Size | 1.90 | 2.39 | 2.60 |
| Households | 3,946 | 14,986 | 124,010,992 |
| Family Households | 1,886 | 8,665 | 80,755,759 |
| Married couple, w/children | 30.0% | 27.0% | 30.5% |
| Married couple, no children | 58.0% | 33.0% | 42.9% |
| Non Family Households | 2,060 | 6,321 | 43,255,233 |
| Single householder, w/children | 2.9% | 24.1% | 15.8% |
| Single householder, no children | 9.2% | 15.9% | 10.8% |