| | Adelphi, MD | New York, NY | United States |
| Population | 16,977 | 8,736,047 | 329,725,481 |
| Female Population | 46.6% | 52.0% | 50.5% |
| Male Population | 53.4% | 48.0% | 49.5% |
| Median Age | 32.6 | 37.3 | 38.4 |
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| Population - 2010 | 15,040 | 8,190,105 | 309,327,143 |
| Population - 2000 | 14,998 | 8,008,278 | 285,036,114 |
| Population - 1990 | 13,524 | 7,322,564 | 251,960,433 |
| Pop. 2000 to Now | 6.3% | 3.1% | 15.6% |
| Pop. 1990 to Now | 17.9% | 12.7% | 30.8% |
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| Population Density | 6,250.7 | 29,083.8 | 93.4 |
| Land Area | 2.7 | 300.4 | 3,531,905.4 |
| Water Area | 0.0 | 167.8 | 264,836.8 |
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| Est. Total Population By Age | | | |
| | Adelphi, MD | New York, NY | United States |
| Age 0 to 4 | 6.8% | 6.2% | 5.9% |
| Age 5 to 9 | 6.9% | 5.5% | 6.1% |
| Age 10 to 14 | 7.7% | 5.8% | 6.6% |
| Age 15 to 17 | 3.7% | 3.3% | 3.9% |
| Age 18 to 20 | 3.9% | 3.2% | 4.0% |
| Age 21 to 24 | 6.5% | 5.0% | 5.2% |
| Age 25 to 34 | 17.5% | 17.3% | 13.8% |
| Age 35 to 44 | 14.2% | 13.8% | 12.9% |
| Age 45 to 54 | 10.6% | 12.5% | 12.6% |
| Age 55 to 59 | 6.8% | 6.3% | 6.7% |
| Age 60 to 64 | 4.5% | 5.8% | 6.3% |
| Age 65 to 74 | 7.2% | 8.7% | 9.6% |
| Age 75 to 84 | 2.5% | 4.4% | 4.5% |
| Age 85 and over | 1.2% | 2.0% | 1.9% |
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| Race | | | |
| | Adelphi, MD | New York, NY | United States |
| White | 11.8% | 31.9% | 59.4% |
| Black | 29.2% | 21.1% | 12.2% |
| Asian | 7.7% | 14.1% | 5.6% |
| Native American | 0.0% | 0.2% | 0.6% |
| Hawaiian, Pacific Islander | 0.0% | 0.0% | 0.2% |
| Other | 0.2% | 1.0% | 0.4% |
| Two or More Races | 0.9% | 2.7% | 3.2% |
| Hispanic | 50.1% | 28.9% | 18.4% |
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| Marriage & Family | | | |
| | Adelphi, MD | New York, NY | United States |
| Married Population | 37.2% | 42.8% | 49.8% |
| Currently Married | 35.7% | 39.9% | 48.0% |
| Married but Separated | 1.5% | 2.9% | 1.8% |
| Single Population | 62.8% | 57.2% | 50.2% |
| Never Married | 53.1% | 43.8% | 33.8% |
| Divorced | 6.5% | 8.1% | 10.8% |
| Widowed | 3.3% | 5.3% | 5.6% |
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| Household Size | 3.20 | 2.63 | 2.60 |
| Households | 5,259 | 3,250,657 | 124,010,992 |
| Family Households | 3,316 | 1,929,690 | 80,755,759 |
| Married couple, w/children | 26.8% | 27.3% | 30.5% |
| Married couple, no children | 27.4% | 34.4% | 42.9% |
| Non Family Households | 1,943 | 1,320,967 | 43,255,233 |
| Single householder, w/children | 29.9% | 19.1% | 15.8% |
| Single householder, no children | 15.8% | 19.2% | 10.8% |