| | St. Joseph, MN | Plymouth, MN | United States |
| Population | 6,919 | 80,034 | 329,725,481 |
| Female Population | 57.0% | 51.0% | 50.5% |
| Male Population | 43.0% | 49.0% | 49.5% |
| Median Age | 26.4 | 40.4 | 38.4 |
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| Population - 2010 | 6,826 | 70,715 | 309,327,143 |
| Population - 2000 | 4,681 | 65,894 | 285,036,114 |
| Population - 1990 | 3,294 | 50,889 | 251,960,433 |
| Pop. 2000 to Now | 65.8% | 20.9% | 15.6% |
| Pop. 1990 to Now | 135.7% | 56.5% | 30.8% |
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| Population Density | 1,757.9 | 2,446.6 | 93.4 |
| Land Area | 3.9 | 32.7 | 3,531,905.4 |
| Water Area | 0.0 | 2.8 | 264,836.8 |
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| Est. Total Population By Age | | | |
| | St. Joseph, MN | Plymouth, MN | United States |
| Age 0 to 4 | 5.3% | 6.9% | 5.9% |
| Age 5 to 9 | 8.7% | 6.8% | 6.1% |
| Age 10 to 14 | 4.5% | 6.5% | 6.6% |
| Age 15 to 17 | 1.2% | 3.8% | 3.9% |
| Age 18 to 20 | 17.3% | 2.2% | 4.0% |
| Age 21 to 24 | 11.9% | 3.2% | 5.2% |
| Age 25 to 34 | 13.5% | 12.3% | 13.8% |
| Age 35 to 44 | 9.5% | 15.5% | 12.9% |
| Age 45 to 54 | 9.9% | 12.5% | 12.6% |
| Age 55 to 59 | 4.2% | 8.1% | 6.7% |
| Age 60 to 64 | 5.1% | 6.3% | 6.3% |
| Age 65 to 74 | 5.4% | 9.5% | 9.6% |
| Age 75 to 84 | 2.5% | 4.6% | 4.5% |
| Age 85 and over | 1.1% | 1.7% | 1.9% |
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| Race | | | |
| | St. Joseph, MN | Plymouth, MN | United States |
| White | 87.2% | 74.2% | 59.4% |
| Black | 5.8% | 4.8% | 12.2% |
| Asian | 1.3% | 10.8% | 5.6% |
| Native American | 0.0% | 0.2% | 0.6% |
| Hawaiian, Pacific Islander | 0.3% | 0.1% | 0.2% |
| Other | 0.0% | 0.7% | 0.4% |
| Two or More Races | 3.2% | 4.5% | 3.2% |
| Hispanic | 2.2% | 4.6% | 18.4% |
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| Marriage & Family | | | |
| | St. Joseph, MN | Plymouth, MN | United States |
| Married Population | 34.5% | 60.8% | 49.8% |
| Currently Married | 34.4% | 60.3% | 48.0% |
| Married but Separated | 0.1% | 0.5% | 1.8% |
| Single Population | 65.5% | 39.2% | 50.2% |
| Never Married | 56.5% | 26.4% | 33.8% |
| Divorced | 7.5% | 8.7% | 10.8% |
| Widowed | 1.4% | 4.1% | 5.6% |
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| Household Size | 2.51 | 2.47 | 2.60 |
| Households | 2,105 | 32,118 | 124,010,992 |
| Family Households | 1,269 | 21,877 | 80,755,759 |
| Married couple, w/children | 27.7% | 38.7% | 30.5% |
| Married couple, no children | 41.6% | 46.1% | 42.9% |
| Non Family Households | 836 | 10,241 | 43,255,233 |
| Single householder, w/children | 20.7% | 8.6% | 15.8% |
| Single householder, no children | 10.0% | 6.6% | 10.8% |