| | St. Francis, WI | Cudahy, WI | United States |
| Population | 9,254 | 18,197 | 329,725,481 |
| Female Population | 52.1% | 51.4% | 50.5% |
| Male Population | 47.9% | 48.6% | 49.5% |
| Median Age | 48.6 | 44.4 | 38.4 |
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| Population - 2010 | 9,325 | 18,327 | 309,327,143 |
| Population - 2000 | 8,662 | 18,429 | 285,036,114 |
| Population - 1990 | 9,245 | 18,659 | 251,960,433 |
| Pop. 2000 to Now | 12.3% | -1.9% | 15.6% |
| Pop. 1990 to Now | 5.2% | -3.1% | 30.8% |
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| Population Density | 3,602.2 | 3,813.3 | 93.4 |
| Land Area | 2.6 | 4.8 | 3,531,905.4 |
| Water Area | 0.0 | 0.0 | 264,836.8 |
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| Est. Total Population By Age | | | |
| | St. Francis, WI | Cudahy, WI | United States |
| Age 0 to 4 | 4.4% | 4.4% | 5.9% |
| Age 5 to 9 | 2.4% | 2.7% | 6.1% |
| Age 10 to 14 | 3.6% | 5.6% | 6.6% |
| Age 15 to 17 | 2.8% | 3.0% | 3.9% |
| Age 18 to 20 | 3.8% | 1.7% | 4.0% |
| Age 21 to 24 | 4.0% | 4.0% | 5.2% |
| Age 25 to 34 | 12.9% | 14.7% | 13.8% |
| Age 35 to 44 | 12.1% | 14.5% | 12.9% |
| Age 45 to 54 | 11.5% | 13.0% | 12.6% |
| Age 55 to 59 | 8.7% | 7.4% | 6.7% |
| Age 60 to 64 | 10.8% | 9.0% | 6.3% |
| Age 65 to 74 | 12.4% | 10.9% | 9.6% |
| Age 75 to 84 | 6.5% | 5.7% | 4.5% |
| Age 85 and over | 4.2% | 3.4% | 1.9% |
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| Race | | | |
| | St. Francis, WI | Cudahy, WI | United States |
| White | 79.3% | 80.9% | 59.4% |
| Black | 2.3% | 2.8% | 12.2% |
| Asian | 1.1% | 1.7% | 5.6% |
| Native American | 0.4% | 0.3% | 0.6% |
| Hawaiian, Pacific Islander | 0.0% | 0.0% | 0.2% |
| Other | 0.3% | 0.0% | 0.4% |
| Two or More Races | 0.4% | 3.9% | 3.2% |
| Hispanic | 16.2% | 10.4% | 18.4% |
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| Marriage & Family | | | |
| | St. Francis, WI | Cudahy, WI | United States |
| Married Population | 41.9% | 46.2% | 49.8% |
| Currently Married | 40.6% | 45.0% | 48.0% |
| Married but Separated | 1.2% | 1.2% | 1.8% |
| Single Population | 58.1% | 53.8% | 50.2% |
| Never Married | 36.2% | 34.9% | 33.8% |
| Divorced | 14.0% | 13.1% | 10.8% |
| Widowed | 7.9% | 5.8% | 5.6% |
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| Household Size | 1.90 | 2.10 | 2.60 |
| Households | 4,759 | 8,663 | 124,010,992 |
| Family Households | 1,937 | 4,884 | 80,755,759 |
| Married couple, w/children | 21.8% | 16.6% | 30.5% |
| Married couple, no children | 59.3% | 53.6% | 42.9% |
| Non Family Households | 2,822 | 3,779 | 43,255,233 |
| Single householder, w/children | 10.3% | 17.1% | 15.8% |
| Single householder, no children | 8.6% | 12.8% | 10.8% |