| | St. Peters, MO | Louisville, KY | United States |
| Population | 57,289 | 630,260 | 329,725,481 |
| Female Population | 52.5% | 51.4% | 50.5% |
| Male Population | 47.5% | 48.6% | 49.5% |
| Median Age | 40 | 37.6 | 38.4 |
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| Population - 2010 | 52,798 | 596,518 | 309,327,143 |
| Population - 2000 | 51,381 | 584,729 | 285,036,114 |
| Population - 1990 | 45,779 | 564,366 | 251,960,433 |
| Pop. 2000 to Now | 13.0% | 5.8% | 15.6% |
| Pop. 1990 to Now | 26.8% | 9.6% | 30.8% |
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| Population Density | 2,548.2 | 2,392.8 | 93.4 |
| Land Area | 22.5 | 263.4 | 3,531,905.4 |
| Water Area | 0.0 | 11.8 | 264,836.8 |
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| Est. Total Population By Age | | | |
| | St. Peters, MO | Louisville, KY | United States |
| Age 0 to 4 | 6.4% | 6.2% | 5.9% |
| Age 5 to 9 | 6.1% | 6.0% | 6.1% |
| Age 10 to 14 | 6.9% | 6.4% | 6.6% |
| Age 15 to 17 | 3.2% | 3.8% | 3.9% |
| Age 18 to 20 | 3.2% | 3.9% | 4.0% |
| Age 21 to 24 | 3.9% | 5.2% | 5.2% |
| Age 25 to 34 | 12.6% | 14.8% | 13.8% |
| Age 35 to 44 | 14.4% | 12.8% | 12.9% |
| Age 45 to 54 | 11.8% | 12.3% | 12.6% |
| Age 55 to 59 | 7.9% | 6.7% | 6.7% |
| Age 60 to 64 | 7.0% | 6.7% | 6.3% |
| Age 65 to 74 | 10.4% | 9.3% | 9.6% |
| Age 75 to 84 | 4.0% | 4.2% | 4.5% |
| Age 85 and over | 2.3% | 1.7% | 1.9% |
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| Race | | | |
| | St. Peters, MO | Louisville, KY | United States |
| White | 86.1% | 63.8% | 59.4% |
| Black | 5.8% | 23.5% | 12.2% |
| Asian | 2.5% | 2.7% | 5.6% |
| Native American | 0.1% | 0.1% | 0.6% |
| Hawaiian, Pacific Islander | 0.0% | 0.1% | 0.2% |
| Other | 0.0% | 0.4% | 0.4% |
| Two or More Races | 3.2% | 3.0% | 3.2% |
| Hispanic | 2.3% | 6.5% | 18.4% |
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| Marriage & Family | | | |
| | St. Peters, MO | Louisville, KY | United States |
| Married Population | 57.0% | 44.1% | 49.8% |
| Currently Married | 55.7% | 42.0% | 48.0% |
| Married but Separated | 1.4% | 2.1% | 1.8% |
| Single Population | 43.0% | 55.9% | 50.2% |
| Never Married | 26.0% | 36.9% | 33.8% |
| Divorced | 11.5% | 12.7% | 10.8% |
| Widowed | 5.4% | 6.3% | 5.6% |
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| Household Size | 2.48 | 2.39 | 2.60 |
| Households | 23,051 | 257,758 | 124,010,992 |
| Family Households | 15,100 | 151,846 | 80,755,759 |
| Married couple, w/children | 35.0% | 26.2% | 30.5% |
| Married couple, no children | 46.8% | 39.2% | 42.9% |
| Non Family Households | 7,951 | 105,912 | 43,255,233 |
| Single householder, w/children | 10.9% | 21.0% | 15.8% |
| Single householder, no children | 7.3% | 13.5% | 10.8% |