| | Fitzwilliam, NH | Brentwood, TN | United States |
| Population | 2,341 | 44,354 | 329,725,481 |
| Female Population | 46.1% | 49.1% | 50.5% |
| Male Population | 53.9% | 50.9% | 49.5% |
| Median Age | 49.5 | 43.1 | 38.4 |
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| Population - 2010 | 2,404 | 37,211 | 309,327,143 |
| Population - 2000 | 2,141 | 23,445 | 285,036,114 |
| Population - 1990 | 2,011 | 16,392 | 251,960,433 |
| Pop. 2000 to Now | 11.0% | 82.9% | 15.6% |
| Pop. 1990 to Now | 18.2% | 161.6% | 30.8% |
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| Population Density | 67.6 | 1,079.2 | 93.4 |
| Land Area | 34.6 | 41.1 | 3,531,905.4 |
| Water Area | 1.4 | 0.0 | 264,836.8 |
| space | | | |
| Est. Total Population By Age | | | |
| | Fitzwilliam, NH | Brentwood, TN | United States |
| Age 0 to 4 | 3.4% | 3.7% | 5.9% |
| Age 5 to 9 | 2.2% | 7.0% | 6.1% |
| Age 10 to 14 | 4.0% | 9.4% | 6.6% |
| Age 15 to 17 | 2.5% | 8.6% | 3.9% |
| Age 18 to 20 | 1.5% | 3.5% | 4.0% |
| Age 21 to 24 | 2.6% | 3.7% | 5.2% |
| Age 25 to 34 | 14.0% | 5.1% | 13.8% |
| Age 35 to 44 | 8.5% | 12.1% | 12.9% |
| Age 45 to 54 | 16.0% | 18.3% | 12.6% |
| Age 55 to 59 | 10.5% | 7.3% | 6.7% |
| Age 60 to 64 | 12.9% | 7.1% | 6.3% |
| Age 65 to 74 | 17.0% | 8.8% | 9.6% |
| Age 75 to 84 | 4.4% | 4.2% | 4.5% |
| Age 85 and over | 0.3% | 1.1% | 1.9% |
| space1 | | | |
| Race | | | |
| | Fitzwilliam, NH | Brentwood, TN | United States |
| White | 96.0% | 83.6% | 59.4% |
| Black | 0.0% | 3.1% | 12.2% |
| Asian | 0.6% | 7.7% | 5.6% |
| Native American | 0.0% | 0.0% | 0.6% |
| Hawaiian, Pacific Islander | 0.0% | 0.0% | 0.2% |
| Other | 0.2% | 0.1% | 0.4% |
| Two or More Races | 2.1% | 2.0% | 3.2% |
| Hispanic | 1.2% | 3.5% | 18.4% |
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| Marriage & Family | | | |
| | Fitzwilliam, NH | Brentwood, TN | United States |
| Married Population | 49.9% | 66.6% | 49.8% |
| Currently Married | 49.4% | 66.2% | 48.0% |
| Married but Separated | 0.5% | 0.4% | 1.8% |
| Single Population | 50.1% | 33.4% | 50.2% |
| Never Married | 31.5% | 23.8% | 33.8% |
| Divorced | 14.8% | 6.1% | 10.8% |
| Widowed | 3.8% | 3.5% | 5.6% |
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| Household Size | 2.32 | 3.04 | 2.60 |
| Households | 1,010 | 14,550 | 124,010,992 |
| Family Households | 633 | 12,315 | 80,755,759 |
| Married couple, w/children | 23.7% | 44.6% | 30.5% |
| Married couple, no children | 57.0% | 46.3% | 42.9% |
| Non Family Households | 377 | 2,235 | 43,255,233 |
| Single householder, w/children | 3.0% | 5.3% | 15.8% |
| Single householder, no children | 16.3% | 3.7% | 10.8% |