| | Belmont, NH | Watertown, NY | United States |
| Population | 7,318 | 25,172 | 329,725,481 |
| Female Population | 54.6% | 49.1% | 50.5% |
| Male Population | 45.4% | 50.9% | 49.5% |
| Median Age | 48.1 | 34.4 | 38.4 |
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| Population - 2010 | 7,335 | 26,885 | 309,327,143 |
| Population - 2000 | 6,716 | 26,705 | 285,036,114 |
| Population - 1990 | 5,796 | 29,429 | 251,960,433 |
| Pop. 2000 to Now | 8.9% | -8.9% | 15.6% |
| Pop. 1990 to Now | 26.2% | -17.3% | 30.8% |
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| Population Density | 240.2 | 2,787.0 | 93.4 |
| Land Area | 30.5 | 9.0 | 3,531,905.4 |
| Water Area | 1.9 | 0.4 | 264,836.8 |
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| Est. Total Population By Age | | | |
| | Belmont, NH | Watertown, NY | United States |
| Age 0 to 4 | 3.2% | 8.2% | 5.9% |
| Age 5 to 9 | 5.5% | 7.4% | 6.1% |
| Age 10 to 14 | 7.5% | 5.2% | 6.6% |
| Age 15 to 17 | 4.4% | 2.5% | 3.9% |
| Age 18 to 20 | 2.3% | 2.7% | 4.0% |
| Age 21 to 24 | 2.3% | 7.2% | 5.2% |
| Age 25 to 34 | 9.2% | 17.9% | 13.8% |
| Age 35 to 44 | 12.2% | 12.3% | 12.9% |
| Age 45 to 54 | 13.1% | 11.5% | 12.6% |
| Age 55 to 59 | 11.5% | 6.5% | 6.7% |
| Age 60 to 64 | 9.2% | 4.9% | 6.3% |
| Age 65 to 74 | 13.4% | 7.4% | 9.6% |
| Age 75 to 84 | 4.9% | 4.7% | 4.5% |
| Age 85 and over | 1.5% | 1.6% | 1.9% |
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| Race | | | |
| | Belmont, NH | Watertown, NY | United States |
| White | 95.4% | 79.9% | 59.4% |
| Black | 0.0% | 7.2% | 12.2% |
| Asian | 1.4% | 1.6% | 5.6% |
| Native American | 0.0% | 0.1% | 0.6% |
| Hawaiian, Pacific Islander | 0.0% | 0.0% | 0.2% |
| Other | 0.0% | 0.3% | 0.4% |
| Two or More Races | 1.5% | 3.9% | 3.2% |
| Hispanic | 1.7% | 7.2% | 18.4% |
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| Marriage & Family | | | |
| | Belmont, NH | Watertown, NY | United States |
| Married Population | 62.2% | 44.7% | 49.8% |
| Currently Married | 61.6% | 41.7% | 48.0% |
| Married but Separated | 0.6% | 3.0% | 1.8% |
| Single Population | 37.8% | 55.3% | 50.2% |
| Never Married | 23.8% | 35.7% | 33.8% |
| Divorced | 9.3% | 14.9% | 10.8% |
| Widowed | 4.6% | 4.7% | 5.6% |
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| Household Size | 2.41 | 2.14 | 2.60 |
| Households | 3,035 | 11,407 | 124,010,992 |
| Family Households | 2,121 | 5,850 | 80,755,759 |
| Married couple, w/children | 29.4% | 30.6% | 30.5% |
| Married couple, no children | 58.2% | 35.7% | 42.9% |
| Non Family Households | 914 | 5,557 | 43,255,233 |
| Single householder, w/children | 10.8% | 22.7% | 15.8% |
| Single householder, no children | 1.7% | 10.9% | 10.8% |