| | Greenbelt, MD | Arlington, VA | United States |
| Population | 24,602 | 235,764 | 329,725,481 |
| Female Population | 54.0% | 49.7% | 50.5% |
| Male Population | 46.0% | 50.3% | 49.5% |
| Median Age | 36.2 | 35.1 | 38.4 |
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| Population - 2010 | 22,187 | 197,467 | 309,327,143 |
| Population - 2000 | 21,456 | 189,453 | 285,036,114 |
| Population - 1990 | 21,096 | 170,936 | 251,960,433 |
| Pop. 2000 to Now | 8.3% | 27.1% | 15.6% |
| Pop. 1990 to Now | 10.1% | 40.9% | 30.8% |
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| Population Density | 3,946.4 | 9,068.9 | 93.4 |
| Land Area | 6.2 | 26.0 | 3,531,905.4 |
| Water Area | 0.1 | 0.1 | 264,836.8 |
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| Est. Total Population By Age | | | |
| | Greenbelt, MD | Arlington, VA | United States |
| Age 0 to 4 | 6.4% | 5.6% | 5.9% |
| Age 5 to 9 | 7.2% | 4.8% | 6.1% |
| Age 10 to 14 | 6.5% | 5.1% | 6.6% |
| Age 15 to 17 | 3.1% | 2.6% | 3.9% |
| Age 18 to 20 | 4.1% | 2.0% | 4.0% |
| Age 21 to 24 | 4.2% | 6.2% | 5.2% |
| Age 25 to 34 | 16.5% | 23.4% | 13.8% |
| Age 35 to 44 | 13.7% | 16.6% | 12.9% |
| Age 45 to 54 | 12.0% | 12.8% | 12.6% |
| Age 55 to 59 | 6.6% | 5.4% | 6.7% |
| Age 60 to 64 | 6.6% | 4.5% | 6.3% |
| Age 65 to 74 | 10.4% | 6.7% | 9.6% |
| Age 75 to 84 | 1.9% | 2.9% | 4.5% |
| Age 85 and over | 0.8% | 1.3% | 1.9% |
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| Race | | | |
| | Greenbelt, MD | Arlington, VA | United States |
| White | 22.5% | 60.2% | 59.4% |
| Black | 45.0% | 9.1% | 12.2% |
| Asian | 9.5% | 10.2% | 5.6% |
| Native American | 0.4% | 0.2% | 0.6% |
| Hawaiian, Pacific Islander | 0.0% | 0.0% | 0.2% |
| Other | 0.8% | 0.5% | 0.4% |
| Two or More Races | 3.8% | 4.3% | 3.2% |
| Hispanic | 18.0% | 15.5% | 18.4% |
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| Marriage & Family | | | |
| | Greenbelt, MD | Arlington, VA | United States |
| Married Population | 36.2% | 45.2% | 49.8% |
| Currently Married | 34.3% | 44.1% | 48.0% |
| Married but Separated | 1.9% | 1.1% | 1.8% |
| Single Population | 63.8% | 54.8% | 50.2% |
| Never Married | 46.4% | 44.0% | 33.8% |
| Divorced | 13.1% | 7.8% | 10.8% |
| Widowed | 4.3% | 3.0% | 5.6% |
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| Household Size | 2.38 | 2.12 | 2.60 |
| Households | 10,321 | 109,528 | 124,010,992 |
| Family Households | 5,814 | 49,969 | 80,755,759 |
| Married couple, w/children | 21.5% | 36.2% | 30.5% |
| Married couple, no children | 27.6% | 45.0% | 42.9% |
| Non Family Households | 4,507 | 59,559 | 43,255,233 |
| Single householder, w/children | 26.6% | 8.9% | 15.8% |
| Single householder, no children | 24.3% | 9.8% | 10.8% |