| | St. Joseph, IL | Boise City, ID | United States |
| Population | 3,888 | 231,537 | 329,725,481 |
| Female Population | 54.3% | 49.6% | 50.5% |
| Male Population | 45.7% | 50.4% | 49.5% |
| Median Age | 39.4 | 37.7 | 38.4 |
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| Population - 2010 | 3,994 | 209,586 | 309,327,143 |
| Population - 2000 | 2,912 | 185,787 | 285,036,114 |
| Population - 1990 | 2,052 | 125,738 | 251,960,433 |
| Pop. 2000 to Now | 30.5% | 23.7% | 15.6% |
| Pop. 1990 to Now | 85.2% | 82.7% | 30.8% |
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| Population Density | 1,866.5 | 2,767.4 | 93.4 |
| Land Area | 2.1 | 83.7 | 3,531,905.4 |
| Water Area | 0.0 | 1.0 | 264,836.8 |
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| Est. Total Population By Age | | | |
| | St. Joseph, IL | Boise City, ID | United States |
| Age 0 to 4 | 5.4% | 4.7% | 5.9% |
| Age 5 to 9 | 3.8% | 5.2% | 6.1% |
| Age 10 to 14 | 11.5% | 6.2% | 6.6% |
| Age 15 to 17 | 6.9% | 3.8% | 3.9% |
| Age 18 to 20 | 1.2% | 4.7% | 4.0% |
| Age 21 to 24 | 5.7% | 5.9% | 5.2% |
| Age 25 to 34 | 8.3% | 15.5% | 13.8% |
| Age 35 to 44 | 15.9% | 14.1% | 12.9% |
| Age 45 to 54 | 6.5% | 12.6% | 12.6% |
| Age 55 to 59 | 5.0% | 6.9% | 6.7% |
| Age 60 to 64 | 13.9% | 5.7% | 6.3% |
| Age 65 to 74 | 11.3% | 8.9% | 9.6% |
| Age 75 to 84 | 3.4% | 4.1% | 4.5% |
| Age 85 and over | 1.2% | 1.7% | 1.9% |
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| Race | | | |
| | St. Joseph, IL | Boise City, ID | United States |
| White | 95.0% | 82.1% | 59.4% |
| Black | 0.1% | 1.6% | 12.2% |
| Asian | 2.5% | 3.4% | 5.6% |
| Native American | 0.2% | 0.3% | 0.6% |
| Hawaiian, Pacific Islander | 0.0% | 0.3% | 0.2% |
| Other | 0.0% | 0.3% | 0.4% |
| Two or More Races | 1.0% | 3.3% | 3.2% |
| Hispanic | 1.3% | 8.8% | 18.4% |
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| Marriage & Family | | | |
| | St. Joseph, IL | Boise City, ID | United States |
| Married Population | 54.7% | 47.9% | 49.8% |
| Currently Married | 53.9% | 47.0% | 48.0% |
| Married but Separated | 0.8% | 1.0% | 1.8% |
| Single Population | 45.3% | 52.1% | 50.2% |
| Never Married | 28.0% | 34.8% | 33.8% |
| Divorced | 8.8% | 12.9% | 10.8% |
| Widowed | 8.5% | 4.4% | 5.6% |
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| Household Size | 2.71 | 2.37 | 2.60 |
| Households | 1,431 | 96,395 | 124,010,992 |
| Family Households | 1,021 | 55,525 | 80,755,759 |
| Married couple, w/children | 37.8% | 31.8% | 30.5% |
| Married couple, no children | 35.5% | 46.2% | 42.9% |
| Non Family Households | 410 | 40,870 | 43,255,233 |
| Single householder, w/children | 23.4% | 13.0% | 15.8% |
| Single householder, no children | 3.3% | 8.9% | 10.8% |