| | Somerville, NJ | Hackettstown, NJ | United States |
| Population | 12,453 | 10,221 | 329,725,481 |
| Female Population | 47.7% | 53.1% | 50.5% |
| Male Population | 52.3% | 46.9% | 49.5% |
| Median Age | 36.7 | 38.3 | 38.4 |
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| Population - 2010 | 12,107 | 9,721 | 309,327,143 |
| Population - 2000 | 12,423 | 10,403 | 285,036,114 |
| Population - 1990 | 11,632 | 8,120 | 251,960,433 |
| Pop. 2000 to Now | -2.1% | -9.9% | 15.6% |
| Pop. 1990 to Now | 4.5% | 15.4% | 30.8% |
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| Population Density | 5,326.4 | 2,829.7 | 93.4 |
| Land Area | 2.3 | 3.6 | 3,531,905.4 |
| Water Area | 0.0 | 0.1 | 264,836.8 |
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| Est. Total Population By Age | | | |
| | Somerville, NJ | Hackettstown, NJ | United States |
| Age 0 to 4 | 5.5% | 3.7% | 5.9% |
| Age 5 to 9 | 4.0% | 6.0% | 6.1% |
| Age 10 to 14 | 6.3% | 5.5% | 6.6% |
| Age 15 to 17 | 3.3% | 5.4% | 3.9% |
| Age 18 to 20 | 2.6% | 9.1% | 4.0% |
| Age 21 to 24 | 6.6% | 6.2% | 5.2% |
| Age 25 to 34 | 17.3% | 8.7% | 13.8% |
| Age 35 to 44 | 16.5% | 15.0% | 12.9% |
| Age 45 to 54 | 12.1% | 13.1% | 12.6% |
| Age 55 to 59 | 4.5% | 5.0% | 6.7% |
| Age 60 to 64 | 6.8% | 5.6% | 6.3% |
| Age 65 to 74 | 6.6% | 9.5% | 9.6% |
| Age 75 to 84 | 6.5% | 4.6% | 4.5% |
| Age 85 and over | 1.2% | 2.5% | 1.9% |
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| Race | | | |
| | Somerville, NJ | Hackettstown, NJ | United States |
| White | 51.8% | 69.1% | 59.4% |
| Black | 11.9% | 2.2% | 12.2% |
| Asian | 10.7% | 5.2% | 5.6% |
| Native American | 0.2% | 0.0% | 0.6% |
| Hawaiian, Pacific Islander | 0.0% | 0.0% | 0.2% |
| Other | 0.3% | 0.4% | 0.4% |
| Two or More Races | 2.3% | 2.1% | 3.2% |
| Hispanic | 22.9% | 21.0% | 18.4% |
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| Marriage & Family | | | |
| | Somerville, NJ | Hackettstown, NJ | United States |
| Married Population | 45.5% | 48.7% | 49.8% |
| Currently Married | 43.5% | 46.4% | 48.0% |
| Married but Separated | 1.9% | 2.3% | 1.8% |
| Single Population | 54.5% | 51.3% | 50.2% |
| Never Married | 39.2% | 37.7% | 33.8% |
| Divorced | 9.4% | 9.5% | 10.8% |
| Widowed | 6.0% | 4.1% | 5.6% |
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| Household Size | 2.46 | 2.58 | 2.60 |
| Households | 4,902 | 3,645 | 124,010,992 |
| Family Households | 2,857 | 2,509 | 80,755,759 |
| Married couple, w/children | 34.8% | 36.8% | 30.5% |
| Married couple, no children | 39.0% | 38.5% | 42.9% |
| Non Family Households | 2,045 | 1,136 | 43,255,233 |
| Single householder, w/children | 13.3% | 16.1% | 15.8% |
| Single householder, no children | 12.8% | 8.6% | 10.8% |