| | St. Johns, MI | Saginaw, MI | United States |
| Population | 7,700 | 44,796 | 329,725,481 |
| Female Population | 49.5% | 50.6% | 50.5% |
| Male Population | 50.5% | 49.4% | 49.5% |
| Median Age | 40.1 | 36.1 | 38.4 |
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| Population - 2010 | 7,864 | 51,390 | 309,327,143 |
| Population - 2000 | 7,485 | 61,799 | 285,036,114 |
| Population - 1990 | 7,284 | 69,512 | 251,960,433 |
| Pop. 2000 to Now | 5.6% | -22.6% | 15.6% |
| Pop. 1990 to Now | 8.5% | -31.2% | 30.8% |
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| Population Density | 1,908.3 | 2,622.4 | 93.4 |
| Land Area | 4.0 | 17.1 | 3,531,905.4 |
| Water Area | 0.0 | 0.7 | 264,836.8 |
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| Est. Total Population By Age | | | |
| | St. Johns, MI | Saginaw, MI | United States |
| Age 0 to 4 | 5.2% | 8.0% | 5.9% |
| Age 5 to 9 | 7.8% | 7.1% | 6.1% |
| Age 10 to 14 | 6.9% | 7.5% | 6.6% |
| Age 15 to 17 | 5.6% | 4.2% | 3.9% |
| Age 18 to 20 | 1.8% | 3.5% | 4.0% |
| Age 21 to 24 | 3.1% | 5.1% | 5.2% |
| Age 25 to 34 | 13.3% | 13.4% | 13.8% |
| Age 35 to 44 | 11.6% | 13.3% | 12.9% |
| Age 45 to 54 | 11.1% | 11.5% | 12.6% |
| Age 55 to 59 | 9.4% | 6.2% | 6.7% |
| Age 60 to 64 | 6.3% | 6.4% | 6.3% |
| Age 65 to 74 | 8.4% | 8.4% | 9.6% |
| Age 75 to 84 | 5.3% | 3.3% | 4.5% |
| Age 85 and over | 4.2% | 2.1% | 1.9% |
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| Race | | | |
| | St. Johns, MI | Saginaw, MI | United States |
| White | 91.7% | 35.9% | 59.4% |
| Black | 2.1% | 44.2% | 12.2% |
| Asian | 0.3% | 0.2% | 5.6% |
| Native American | 1.0% | 0.1% | 0.6% |
| Hawaiian, Pacific Islander | 0.0% | 0.0% | 0.2% |
| Other | 0.0% | 0.0% | 0.4% |
| Two or More Races | 2.1% | 4.0% | 3.2% |
| Hispanic | 2.8% | 15.7% | 18.4% |
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| Marriage & Family | | | |
| | St. Johns, MI | Saginaw, MI | United States |
| Married Population | 50.1% | 30.2% | 49.8% |
| Currently Married | 47.7% | 27.8% | 48.0% |
| Married but Separated | 2.4% | 2.4% | 1.8% |
| Single Population | 49.9% | 69.8% | 50.2% |
| Never Married | 30.2% | 48.4% | 33.8% |
| Divorced | 12.4% | 15.3% | 10.8% |
| Widowed | 7.3% | 6.1% | 5.6% |
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| Household Size | 2.44 | 2.40 | 2.60 |
| Households | 2,995 | 18,092 | 124,010,992 |
| Family Households | 1,908 | 9,736 | 80,755,759 |
| Married couple, w/children | 27.4% | 18.5% | 30.5% |
| Married couple, no children | 45.8% | 26.6% | 42.9% |
| Non Family Households | 1,087 | 8,356 | 43,255,233 |
| Single householder, w/children | 20.9% | 35.4% | 15.8% |
| Single householder, no children | 6.0% | 19.4% | 10.8% |