| | Williamstown, NJ | Browns Mills, NJ | United States |
| Population | 14,947 | 10,053 | 329,725,481 |
| Female Population | 53.1% | 52.6% | 50.5% |
| Male Population | 46.9% | 47.4% | 49.5% |
| Median Age | 40.8 | 40.5 | 38.4 |
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| Population - 2010 | 14,232 | 11,129 | 309,327,143 |
| Population - 2000 | 11,812 | 11,257 | 285,036,114 |
| Population - 1990 | 10,891 | 11,903 | 251,960,433 |
| Pop. 2000 to Now | 29.6% | -4.7% | 15.6% |
| Pop. 1990 to Now | 40.6% | -9.8% | 30.8% |
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| Population Density | 2,013.6 | 1,871.0 | 93.4 |
| Land Area | 7.4 | 5.4 | 3,531,905.4 |
| Water Area | 0.0 | 0.2 | 264,836.8 |
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| Est. Total Population By Age | | | |
| | Williamstown, NJ | Browns Mills, NJ | United States |
| Age 0 to 4 | 4.4% | 5.7% | 5.9% |
| Age 5 to 9 | 6.9% | 5.3% | 6.1% |
| Age 10 to 14 | 5.9% | 5.3% | 6.6% |
| Age 15 to 17 | 4.9% | 4.1% | 3.9% |
| Age 18 to 20 | 2.6% | 4.0% | 4.0% |
| Age 21 to 24 | 6.0% | 5.9% | 5.2% |
| Age 25 to 34 | 11.7% | 13.3% | 13.8% |
| Age 35 to 44 | 12.5% | 10.8% | 12.9% |
| Age 45 to 54 | 14.6% | 13.3% | 12.6% |
| Age 55 to 59 | 7.5% | 6.6% | 6.7% |
| Age 60 to 64 | 6.8% | 8.3% | 6.3% |
| Age 65 to 74 | 8.9% | 11.0% | 9.6% |
| Age 75 to 84 | 3.9% | 5.0% | 4.5% |
| Age 85 and over | 3.4% | 1.7% | 1.9% |
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| Race | | | |
| | Williamstown, NJ | Browns Mills, NJ | United States |
| White | 78.5% | 57.5% | 59.4% |
| Black | 9.4% | 17.3% | 12.2% |
| Asian | 1.4% | 4.3% | 5.6% |
| Native American | 0.0% | 0.0% | 0.6% |
| Hawaiian, Pacific Islander | 0.0% | 0.0% | 0.2% |
| Other | 0.0% | 0.0% | 0.4% |
| Two or More Races | 4.7% | 7.0% | 3.2% |
| Hispanic | 6.0% | 13.8% | 18.4% |
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| Marriage & Family | | | |
| | Williamstown, NJ | Browns Mills, NJ | United States |
| Married Population | 51.3% | 43.9% | 49.8% |
| Currently Married | 50.3% | 39.8% | 48.0% |
| Married but Separated | 1.1% | 4.2% | 1.8% |
| Single Population | 48.7% | 56.1% | 50.2% |
| Never Married | 29.6% | 34.8% | 33.8% |
| Divorced | 11.6% | 12.9% | 10.8% |
| Widowed | 7.5% | 8.4% | 5.6% |
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| Household Size | 2.61 | 2.66 | 2.60 |
| Households | 5,661 | 3,771 | 124,010,992 |
| Family Households | 3,803 | 2,447 | 80,755,759 |
| Married couple, w/children | 37.1% | 21.3% | 30.5% |
| Married couple, no children | 40.7% | 40.9% | 42.9% |
| Non Family Households | 1,858 | 1,324 | 43,255,233 |
| Single householder, w/children | 11.8% | 21.7% | 15.8% |
| Single householder, no children | 10.5% | 16.0% | 10.8% |