| | Garrett Park, MD | Washington, DC | United States |
| Population | 864 | 683,154 | 329,725,481 |
| Female Population | 46.3% | 52.4% | 50.5% |
| Male Population | 53.7% | 47.7% | 49.5% |
| Median Age | 50.7 | 34.3 | 38.4 |
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| Population - 2010 | 964 | 605,282 | 309,327,143 |
| Population - 2000 | 917 | 572,059 | 285,036,114 |
| Population - 1990 | 884 | 606,900 | 251,960,433 |
| Pop. 2000 to Now | 10.7% | 24.6% | 15.6% |
| Pop. 1990 to Now | 14.8% | 17.5% | 30.8% |
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| Population Density | 3,375.0 | 11,174.3 | 93.4 |
| Land Area | 0.3 | 61.1 | 3,531,905.4 |
| Water Area | 0.0 | 7.2 | 264,836.8 |
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| Est. Total Population By Age | | | |
| | Garrett Park, MD | Washington, DC | United States |
| Age 0 to 4 | 3.4% | 6.3% | 5.9% |
| Age 5 to 9 | 8.0% | 5.1% | 6.1% |
| Age 10 to 14 | 5.7% | 4.6% | 6.6% |
| Age 15 to 17 | 4.5% | 2.3% | 3.9% |
| Age 18 to 20 | 3.6% | 4.5% | 4.0% |
| Age 21 to 24 | 3.8% | 5.8% | 5.2% |
| Age 25 to 34 | 3.7% | 22.8% | 13.8% |
| Age 35 to 44 | 10.3% | 15.6% | 12.9% |
| Age 45 to 54 | 16.1% | 10.8% | 12.6% |
| Age 55 to 59 | 8.2% | 5.2% | 6.7% |
| Age 60 to 64 | 7.8% | 4.9% | 6.3% |
| Age 65 to 74 | 16.1% | 7.2% | 9.6% |
| Age 75 to 84 | 8.1% | 3.5% | 4.5% |
| Age 85 and over | 0.8% | 1.5% | 1.9% |
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| Race | | | |
| | Garrett Park, MD | Washington, DC | United States |
| White | 89.6% | 36.7% | 59.4% |
| Black | 0.0% | 43.9% | 12.2% |
| Asian | 5.9% | 4.0% | 5.6% |
| Native American | 0.0% | 0.1% | 0.6% |
| Hawaiian, Pacific Islander | 0.0% | 0.0% | 0.2% |
| Other | 0.0% | 0.5% | 0.4% |
| Two or More Races | 1.9% | 3.5% | 3.2% |
| Hispanic | 2.7% | 11.3% | 18.4% |
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| Marriage & Family | | | |
| | Garrett Park, MD | Washington, DC | United States |
| Married Population | 66.0% | 32.6% | 49.8% |
| Currently Married | 65.0% | 30.9% | 48.0% |
| Married but Separated | 1.0% | 1.7% | 1.8% |
| Single Population | 34.0% | 67.4% | 50.2% |
| Never Married | 22.3% | 55.8% | 33.8% |
| Divorced | 5.2% | 8.2% | 10.8% |
| Widowed | 6.6% | 3.5% | 5.6% |
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| Household Size | 2.57 | 2.08 | 2.60 |
| Households | 336 | 310,104 | 124,010,992 |
| Family Households | 266 | 131,196 | 80,755,759 |
| Married couple, w/children | 35.3% | 24.1% | 30.5% |
| Married couple, no children | 51.9% | 36.8% | 42.9% |
| Non Family Households | 70 | 178,908 | 43,255,233 |
| Single householder, w/children | 6.0% | 22.8% | 15.8% |
| Single householder, no children | 6.8% | 16.2% | 10.8% |