| | Lexington, KY | St. Peters, MO | United States |
| Population | 321,354 | 57,289 | 329,725,481 |
| Female Population | 50.8% | 52.5% | 50.5% |
| Male Population | 49.2% | 47.5% | 49.5% |
| Median Age | 35 | 40 | 38.4 |
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| Population - 2010 | 296,868 | 52,798 | 309,327,143 |
| Population - 2000 | 260,512 | 51,381 | 285,036,114 |
| Population - 1990 | 225,089 | 45,779 | 251,960,433 |
| Pop. 2000 to Now | 24.7% | 13.0% | 15.6% |
| Pop. 1990 to Now | 44.3% | 26.8% | 30.8% |
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| Population Density | 1,133.0 | 2,548.2 | 93.4 |
| Land Area | 283.6 | 22.5 | 3,531,905.4 |
| Water Area | 1.9 | 0.0 | 264,836.8 |
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| Est. Total Population By Age | | | |
| | Lexington, KY | St. Peters, MO | United States |
| Age 0 to 4 | 5.9% | 6.4% | 5.9% |
| Age 5 to 9 | 6.0% | 6.1% | 6.1% |
| Age 10 to 14 | 5.7% | 6.9% | 6.6% |
| Age 15 to 17 | 3.4% | 3.2% | 3.9% |
| Age 18 to 20 | 5.8% | 3.2% | 4.0% |
| Age 21 to 24 | 8.1% | 3.9% | 5.2% |
| Age 25 to 34 | 15.2% | 12.6% | 13.8% |
| Age 35 to 44 | 13.2% | 14.4% | 12.9% |
| Age 45 to 54 | 11.7% | 11.8% | 12.6% |
| Age 55 to 59 | 5.9% | 7.9% | 6.7% |
| Age 60 to 64 | 5.6% | 7.0% | 6.3% |
| Age 65 to 74 | 8.3% | 10.4% | 9.6% |
| Age 75 to 84 | 3.8% | 4.0% | 4.5% |
| Age 85 and over | 1.4% | 2.3% | 1.9% |
| space1 | | | |
| Race | | | |
| | Lexington, KY | St. Peters, MO | United States |
| White | 70.0% | 86.1% | 59.4% |
| Black | 14.5% | 5.8% | 12.2% |
| Asian | 4.0% | 2.5% | 5.6% |
| Native American | 0.1% | 0.1% | 0.6% |
| Hawaiian, Pacific Islander | 0.0% | 0.0% | 0.2% |
| Other | 0.4% | 0.0% | 0.4% |
| Two or More Races | 3.7% | 3.2% | 3.2% |
| Hispanic | 7.4% | 2.3% | 18.4% |
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| Marriage & Family | | | |
| | Lexington, KY | St. Peters, MO | United States |
| Married Population | 45.0% | 57.0% | 49.8% |
| Currently Married | 43.4% | 55.7% | 48.0% |
| Married but Separated | 1.5% | 1.4% | 1.8% |
| Single Population | 55.0% | 43.0% | 50.2% |
| Never Married | 38.6% | 26.0% | 33.8% |
| Divorced | 11.8% | 11.5% | 10.8% |
| Widowed | 4.6% | 5.4% | 5.6% |
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| Household Size | 2.30 | 2.48 | 2.60 |
| Households | 134,229 | 23,051 | 124,010,992 |
| Family Households | 75,187 | 15,100 | 80,755,759 |
| Married couple, w/children | 31.0% | 35.0% | 30.5% |
| Married couple, no children | 41.2% | 46.8% | 42.9% |
| Non Family Households | 59,042 | 7,951 | 43,255,233 |
| Single householder, w/children | 17.4% | 10.9% | 15.8% |
| Single householder, no children | 10.4% | 7.3% | 10.8% |