| | Killeen, TX | Washington, DC | United States |
| Population | 150,082 | 683,154 | 329,725,481 |
| Female Population | 50.8% | 52.4% | 50.5% |
| Male Population | 49.2% | 47.7% | 49.5% |
| Median Age | 29.6 | 34.3 | 38.4 |
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| Population - 2010 | 129,020 | 605,282 | 309,327,143 |
| Population - 2000 | 86,911 | 572,059 | 285,036,114 |
| Population - 1990 | 63,535 | 606,900 | 251,960,433 |
| Pop. 2000 to Now | 77.2% | 24.6% | 15.6% |
| Pop. 1990 to Now | 142.4% | 17.5% | 30.8% |
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| Population Density | 2,755.1 | 11,174.3 | 93.4 |
| Land Area | 54.5 | 61.1 | 3,531,905.4 |
| Water Area | 0.7 | 7.2 | 264,836.8 |
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| Est. Total Population By Age | | | |
| | Killeen, TX | Washington, DC | United States |
| Age 0 to 4 | 9.7% | 6.3% | 5.9% |
| Age 5 to 9 | 7.9% | 5.1% | 6.1% |
| Age 10 to 14 | 7.9% | 4.6% | 6.6% |
| Age 15 to 17 | 4.4% | 2.3% | 3.9% |
| Age 18 to 20 | 3.9% | 4.5% | 4.0% |
| Age 21 to 24 | 6.9% | 5.8% | 5.2% |
| Age 25 to 34 | 18.8% | 22.8% | 13.8% |
| Age 35 to 44 | 14.1% | 15.6% | 12.9% |
| Age 45 to 54 | 10.6% | 10.8% | 12.6% |
| Age 55 to 59 | 4.7% | 5.2% | 6.7% |
| Age 60 to 64 | 4.0% | 4.9% | 6.3% |
| Age 65 to 74 | 4.8% | 7.2% | 9.6% |
| Age 75 to 84 | 1.6% | 3.5% | 4.5% |
| Age 85 and over | 0.6% | 1.5% | 1.9% |
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| Race | | | |
| | Killeen, TX | Washington, DC | United States |
| White | 26.2% | 36.7% | 59.4% |
| Black | 34.9% | 43.9% | 12.2% |
| Asian | 4.0% | 4.0% | 5.6% |
| Native American | 0.3% | 0.1% | 0.6% |
| Hawaiian, Pacific Islander | 0.9% | 0.0% | 0.2% |
| Other | 0.3% | 0.5% | 0.4% |
| Two or More Races | 5.8% | 3.5% | 3.2% |
| Hispanic | 27.7% | 11.3% | 18.4% |
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| Marriage & Family | | | |
| | Killeen, TX | Washington, DC | United States |
| Married Population | 50.8% | 32.6% | 49.8% |
| Currently Married | 48.1% | 30.9% | 48.0% |
| Married but Separated | 2.6% | 1.7% | 1.8% |
| Single Population | 49.2% | 67.4% | 50.2% |
| Never Married | 33.9% | 55.8% | 33.8% |
| Divorced | 10.7% | 8.2% | 10.8% |
| Widowed | 4.6% | 3.5% | 5.6% |
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| Household Size | 2.69 | 2.08 | 2.60 |
| Households | 55,759 | 310,104 | 124,010,992 |
| Family Households | 37,111 | 131,196 | 80,755,759 |
| Married couple, w/children | 32.0% | 24.1% | 30.5% |
| Married couple, no children | 32.9% | 36.8% | 42.9% |
| Non Family Households | 18,648 | 178,908 | 43,255,233 |
| Single householder, w/children | 27.2% | 22.8% | 15.8% |
| Single householder, no children | 8.0% | 16.2% | 10.8% |