| | Washington, DC | Fairfield, CA | United States |
| Population | 683,154 | 118,932 | 329,725,481 |
| Female Population | 52.4% | 50.1% | 50.5% |
| Male Population | 47.7% | 49.9% | 49.5% |
| Median Age | 34.3 | 35.2 | 38.4 |
| space3 | | | |
| Population - 2010 | 605,282 | 105,652 | 309,327,143 |
| Population - 2000 | 572,059 | 96,178 | 285,036,114 |
| Population - 1990 | 606,900 | 77,211 | 251,960,433 |
| Pop. 2000 to Now | 24.6% | 22.3% | 15.6% |
| Pop. 1990 to Now | 17.5% | 52.3% | 30.8% |
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| Population Density | 11,174.3 | 2,899.5 | 93.4 |
| Land Area | 61.1 | 41.0 | 3,531,905.4 |
| Water Area | 7.2 | 0.3 | 264,836.8 |
| space | | | |
| Est. Total Population By Age | | | |
| | Washington, DC | Fairfield, CA | United States |
| Age 0 to 4 | 6.3% | 7.4% | 5.9% |
| Age 5 to 9 | 5.1% | 6.2% | 6.1% |
| Age 10 to 14 | 4.6% | 7.6% | 6.6% |
| Age 15 to 17 | 2.3% | 4.1% | 3.9% |
| Age 18 to 20 | 4.5% | 3.6% | 4.0% |
| Age 21 to 24 | 5.8% | 5.4% | 5.2% |
| Age 25 to 34 | 22.8% | 15.5% | 13.8% |
| Age 35 to 44 | 15.6% | 13.7% | 12.9% |
| Age 45 to 54 | 10.8% | 12.3% | 12.6% |
| Age 55 to 59 | 5.2% | 5.7% | 6.7% |
| Age 60 to 64 | 4.9% | 5.5% | 6.3% |
| Age 65 to 74 | 7.2% | 7.8% | 9.6% |
| Age 75 to 84 | 3.5% | 3.7% | 4.5% |
| Age 85 and over | 1.5% | 1.5% | 1.9% |
| space1 | | | |
| Race | | | |
| | Washington, DC | Fairfield, CA | United States |
| White | 36.7% | 29.0% | 59.4% |
| Black | 43.9% | 15.6% | 12.2% |
| Asian | 4.0% | 17.4% | 5.6% |
| Native American | 0.1% | 0.5% | 0.6% |
| Hawaiian, Pacific Islander | 0.0% | 1.2% | 0.2% |
| Other | 0.5% | 0.4% | 0.4% |
| Two or More Races | 3.5% | 6.7% | 3.2% |
| Hispanic | 11.3% | 29.3% | 18.4% |
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| Marriage & Family | | | |
| | Washington, DC | Fairfield, CA | United States |
| Married Population | 32.6% | 51.5% | 49.8% |
| Currently Married | 30.9% | 49.2% | 48.0% |
| Married but Separated | 1.7% | 2.3% | 1.8% |
| Single Population | 67.4% | 48.5% | 50.2% |
| Never Married | 55.8% | 35.1% | 33.8% |
| Divorced | 8.2% | 8.6% | 10.8% |
| Widowed | 3.5% | 4.9% | 5.6% |
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| Household Size | 2.08 | 3.16 | 2.60 |
| Households | 310,104 | 37,176 | 124,010,992 |
| Family Households | 131,196 | 28,037 | 80,755,759 |
| Married couple, w/children | 24.1% | 34.1% | 30.5% |
| Married couple, no children | 36.8% | 37.1% | 42.9% |
| Non Family Households | 178,908 | 9,139 | 43,255,233 |
| Single householder, w/children | 22.8% | 17.8% | 15.8% |
| Single householder, no children | 16.2% | 11.0% | 10.8% |