| | Leonia, NJ | Crofton, MD | United States |
| Population | 9,283 | 29,812 | 329,725,481 |
| Female Population | 51.2% | 49.9% | 50.5% |
| Male Population | 48.8% | 50.1% | 49.5% |
| Median Age | 46.1 | 36.4 | 38.4 |
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| Population - 2010 | 8,954 | 27,624 | 309,327,143 |
| Population - 2000 | 8,914 | 20,091 | 285,036,114 |
| Population - 1990 | 8,365 | 12,781 | 251,960,433 |
| Pop. 2000 to Now | 0.8% | 45.7% | 15.6% |
| Pop. 1990 to Now | 7.5% | 129.0% | 30.8% |
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| Population Density | 6,095.2 | 4,508.1 | 93.4 |
| Land Area | 1.5 | 6.6 | 3,531,905.4 |
| Water Area | 0.1 | 0.0 | 264,836.8 |
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| Est. Total Population By Age | | | |
| | Leonia, NJ | Crofton, MD | United States |
| Age 0 to 4 | 6.0% | 6.9% | 5.9% |
| Age 5 to 9 | 5.0% | 7.6% | 6.1% |
| Age 10 to 14 | 6.2% | 10.4% | 6.6% |
| Age 15 to 17 | 4.3% | 4.3% | 3.9% |
| Age 18 to 20 | 2.5% | 3.1% | 4.0% |
| Age 21 to 24 | 3.8% | 2.7% | 5.2% |
| Age 25 to 34 | 9.2% | 13.5% | 13.8% |
| Age 35 to 44 | 11.9% | 15.9% | 12.9% |
| Age 45 to 54 | 14.8% | 14.0% | 12.6% |
| Age 55 to 59 | 8.2% | 5.9% | 6.7% |
| Age 60 to 64 | 10.0% | 4.7% | 6.3% |
| Age 65 to 74 | 10.1% | 7.0% | 9.6% |
| Age 75 to 84 | 6.2% | 3.7% | 4.5% |
| Age 85 and over | 1.8% | 0.5% | 1.9% |
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| Race | | | |
| | Leonia, NJ | Crofton, MD | United States |
| White | 32.0% | 62.4% | 59.4% |
| Black | 2.8% | 15.2% | 12.2% |
| Asian | 38.5% | 8.5% | 5.6% |
| Native American | 0.1% | 0.0% | 0.6% |
| Hawaiian, Pacific Islander | 0.3% | 0.0% | 0.2% |
| Other | 0.7% | 0.1% | 0.4% |
| Two or More Races | 2.4% | 5.8% | 3.2% |
| Hispanic | 23.2% | 8.0% | 18.4% |
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| Marriage & Family | | | |
| | Leonia, NJ | Crofton, MD | United States |
| Married Population | 63.9% | 56.9% | 49.8% |
| Currently Married | 62.7% | 55.7% | 48.0% |
| Married but Separated | 1.3% | 1.3% | 1.8% |
| Single Population | 36.1% | 43.1% | 50.2% |
| Never Married | 23.2% | 28.4% | 33.8% |
| Divorced | 7.0% | 10.4% | 10.8% |
| Widowed | 5.9% | 4.3% | 5.6% |
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| Household Size | 2.67 | 2.83 | 2.60 |
| Households | 3,470 | 10,483 | 124,010,992 |
| Family Households | 2,468 | 7,738 | 80,755,759 |
| Married couple, w/children | 37.6% | 40.8% | 30.5% |
| Married couple, no children | 48.3% | 35.2% | 42.9% |
| Non Family Households | 1,002 | 2,745 | 43,255,233 |
| Single householder, w/children | 6.5% | 16.9% | 15.8% |
| Single householder, no children | 7.6% | 7.1% | 10.8% |