| | El Cajon, CA | Richmond, KY | United States |
| Population | 106,043 | 34,662 | 329,725,481 |
| Female Population | 50.8% | 52.4% | 50.5% |
| Male Population | 49.3% | 47.6% | 49.5% |
| Median Age | 34.8 | 26.3 | 38.4 |
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| Population - 2010 | 99,815 | 31,694 | 309,327,143 |
| Population - 2000 | 94,869 | 27,152 | 285,036,114 |
| Population - 1990 | 88,693 | 21,155 | 251,960,433 |
| Pop. 2000 to Now | 7.9% | 35.5% | 15.6% |
| Pop. 1990 to Now | 15.5% | 74.0% | 30.8% |
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| Population Density | 7,320.9 | 1,705.6 | 93.4 |
| Land Area | 14.5 | 20.3 | 3,531,905.4 |
| Water Area | 0.0 | 0.3 | 264,836.8 |
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| Est. Total Population By Age | | | |
| | El Cajon, CA | Richmond, KY | United States |
| Age 0 to 4 | 7.2% | 5.0% | 5.9% |
| Age 5 to 9 | 6.6% | 5.0% | 6.1% |
| Age 10 to 14 | 7.4% | 4.8% | 6.6% |
| Age 15 to 17 | 4.2% | 2.8% | 3.9% |
| Age 18 to 20 | 3.9% | 13.0% | 4.0% |
| Age 21 to 24 | 5.3% | 15.9% | 5.2% |
| Age 25 to 34 | 15.7% | 14.9% | 13.8% |
| Age 35 to 44 | 14.0% | 12.2% | 12.9% |
| Age 45 to 54 | 10.9% | 7.8% | 12.6% |
| Age 55 to 59 | 5.8% | 3.6% | 6.7% |
| Age 60 to 64 | 6.2% | 3.9% | 6.3% |
| Age 65 to 74 | 7.9% | 5.9% | 9.6% |
| Age 75 to 84 | 3.4% | 3.5% | 4.5% |
| Age 85 and over | 1.6% | 1.6% | 1.9% |
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| Race | | | |
| | El Cajon, CA | Richmond, KY | United States |
| White | 56.7% | 86.0% | 59.4% |
| Black | 6.2% | 6.0% | 12.2% |
| Asian | 4.3% | 1.3% | 5.6% |
| Native American | 0.1% | 0.2% | 0.6% |
| Hawaiian, Pacific Islander | 0.5% | 0.5% | 0.2% |
| Other | 0.4% | 0.1% | 0.4% |
| Two or More Races | 4.7% | 2.9% | 3.2% |
| Hispanic | 27.1% | 3.0% | 18.4% |
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| Marriage & Family | | | |
| | El Cajon, CA | Richmond, KY | United States |
| Married Population | 46.3% | 34.1% | 49.8% |
| Currently Married | 43.9% | 31.5% | 48.0% |
| Married but Separated | 2.4% | 2.6% | 1.8% |
| Single Population | 53.7% | 65.9% | 50.2% |
| Never Married | 37.6% | 47.1% | 33.8% |
| Divorced | 10.5% | 14.4% | 10.8% |
| Widowed | 5.7% | 4.4% | 5.6% |
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| Household Size | 2.96 | 2.19 | 2.60 |
| Households | 35,003 | 13,804 | 124,010,992 |
| Family Households | 25,018 | 6,475 | 80,755,759 |
| Married couple, w/children | 34.1% | 26.4% | 30.5% |
| Married couple, no children | 30.9% | 38.3% | 42.9% |
| Non Family Households | 9,985 | 7,329 | 43,255,233 |
| Single householder, w/children | 20.4% | 25.3% | 15.8% |
| Single householder, no children | 14.6% | 10.0% | 10.8% |