| | Flemington, NJ | Mahwah, NJ | United States |
| Population | 4,819 | 25,530 | 329,725,481 |
| Female Population | 53.1% | 52.6% | 50.5% |
| Male Population | 46.9% | 47.4% | 49.5% |
| Median Age | 32.6 | 44 | 38.4 |
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| Population - 2010 | 4,581 | 25,912 | 309,327,143 |
| Population - 2000 | 4,200 | 24,062 | 285,036,114 |
| Population - 1990 | 4,047 | 17,905 | 251,960,433 |
| Pop. 2000 to Now | 8.4% | 8.4% | 15.6% |
| Pop. 1990 to Now | 12.5% | 45.7% | 30.8% |
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| Population Density | 4,474.5 | 993.6 | 93.4 |
| Land Area | 1.1 | 25.7 | 3,531,905.4 |
| Water Area | 0.0 | 0.5 | 264,836.8 |
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| Est. Total Population By Age | | | |
| | Flemington, NJ | Mahwah, NJ | United States |
| Age 0 to 4 | 6.9% | 4.1% | 5.9% |
| Age 5 to 9 | 6.9% | 4.8% | 6.1% |
| Age 10 to 14 | 5.7% | 6.3% | 6.6% |
| Age 15 to 17 | 2.4% | 4.7% | 3.9% |
| Age 18 to 20 | 6.2% | 8.5% | 4.0% |
| Age 21 to 24 | 6.8% | 6.8% | 5.2% |
| Age 25 to 34 | 18.9% | 5.7% | 13.8% |
| Age 35 to 44 | 14.7% | 11.1% | 12.9% |
| Age 45 to 54 | 9.7% | 14.7% | 12.6% |
| Age 55 to 59 | 5.3% | 6.8% | 6.7% |
| Age 60 to 64 | 5.9% | 7.0% | 6.3% |
| Age 65 to 74 | 8.2% | 12.0% | 9.6% |
| Age 75 to 84 | 1.8% | 6.0% | 4.5% |
| Age 85 and over | 0.7% | 1.6% | 1.9% |
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| Race | | | |
| | Flemington, NJ | Mahwah, NJ | United States |
| White | 54.3% | 70.0% | 59.4% |
| Black | 4.9% | 2.1% | 12.2% |
| Asian | 6.7% | 12.5% | 5.6% |
| Native American | 0.0% | 0.2% | 0.6% |
| Hawaiian, Pacific Islander | 0.0% | 0.0% | 0.2% |
| Other | 3.3% | 0.1% | 0.4% |
| Two or More Races | 1.1% | 2.5% | 3.2% |
| Hispanic | 29.7% | 12.6% | 18.4% |
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| Marriage & Family | | | |
| | Flemington, NJ | Mahwah, NJ | United States |
| Married Population | 52.1% | 51.6% | 49.8% |
| Currently Married | 50.2% | 50.5% | 48.0% |
| Married but Separated | 1.9% | 1.1% | 1.8% |
| Single Population | 47.9% | 48.4% | 50.2% |
| Never Married | 33.3% | 35.9% | 33.8% |
| Divorced | 10.4% | 7.0% | 10.8% |
| Widowed | 4.2% | 5.5% | 5.6% |
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| Household Size | 2.68 | 2.46 | 2.60 |
| Households | 1,757 | 9,430 | 124,010,992 |
| Family Households | 1,078 | 6,154 | 80,755,759 |
| Married couple, w/children | 40.0% | 32.3% | 30.5% |
| Married couple, no children | 39.4% | 52.7% | 42.9% |
| Non Family Households | 679 | 3,276 | 43,255,233 |
| Single householder, w/children | 8.2% | 8.0% | 15.8% |
| Single householder, no children | 12.4% | 7.0% | 10.8% |