| | Merrimack, NH | Winchester, VA | United States |
| Population | 26,762 | 28,194 | 329,725,481 |
| Female Population | 50.0% | 51.1% | 50.5% |
| Male Population | 50.0% | 48.9% | 49.5% |
| Median Age | 42.1 | 36.6 | 38.4 |
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| Population - 2010 | 25,507 | 26,150 | 309,327,143 |
| Population - 2000 | 25,119 | 23,585 | 285,036,114 |
| Population - 1990 | 22,156 | 21,947 | 251,960,433 |
| Pop. 2000 to Now | 9.3% | 17.5% | 15.6% |
| Pop. 1990 to Now | 23.9% | 26.2% | 30.8% |
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| Population Density | 822.7 | 3,066.9 | 93.4 |
| Land Area | 32.5 | 9.2 | 3,531,905.4 |
| Water Area | 0.9 | 0.0 | 264,836.8 |
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| Est. Total Population By Age | | | |
| | Merrimack, NH | Winchester, VA | United States |
| Age 0 to 4 | 5.2% | 6.1% | 5.9% |
| Age 5 to 9 | 4.9% | 6.4% | 6.1% |
| Age 10 to 14 | 8.3% | 6.2% | 6.6% |
| Age 15 to 17 | 4.4% | 4.1% | 3.9% |
| Age 18 to 20 | 3.5% | 5.7% | 4.0% |
| Age 21 to 24 | 3.2% | 4.7% | 5.2% |
| Age 25 to 34 | 12.7% | 13.8% | 13.8% |
| Age 35 to 44 | 12.0% | 12.3% | 12.9% |
| Age 45 to 54 | 13.8% | 12.3% | 12.6% |
| Age 55 to 59 | 8.3% | 6.4% | 6.7% |
| Age 60 to 64 | 6.8% | 5.6% | 6.3% |
| Age 65 to 74 | 11.2% | 9.4% | 9.6% |
| Age 75 to 84 | 4.7% | 5.1% | 4.5% |
| Age 85 and over | 1.0% | 1.7% | 1.9% |
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| Race | | | |
| | Merrimack, NH | Winchester, VA | United States |
| White | 86.4% | 64.5% | 59.4% |
| Black | 1.1% | 9.5% | 12.2% |
| Asian | 4.4% | 2.1% | 5.6% |
| Native American | 0.0% | 0.2% | 0.6% |
| Hawaiian, Pacific Islander | 0.0% | 0.0% | 0.2% |
| Other | 0.4% | 0.9% | 0.4% |
| Two or More Races | 2.7% | 4.7% | 3.2% |
| Hispanic | 5.0% | 18.2% | 18.4% |
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| Marriage & Family | | | |
| | Merrimack, NH | Winchester, VA | United States |
| Married Population | 58.0% | 42.9% | 49.8% |
| Currently Married | 57.4% | 40.5% | 48.0% |
| Married but Separated | 0.6% | 2.4% | 1.8% |
| Single Population | 42.0% | 57.1% | 50.2% |
| Never Married | 27.5% | 37.7% | 33.8% |
| Divorced | 10.7% | 13.7% | 10.8% |
| Widowed | 3.8% | 5.7% | 5.6% |
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| Household Size | 2.66 | 2.47 | 2.60 |
| Households | 10,009 | 11,018 | 124,010,992 |
| Family Households | 7,271 | 6,026 | 80,755,759 |
| Married couple, w/children | 31.9% | 26.2% | 30.5% |
| Married couple, no children | 52.7% | 40.8% | 42.9% |
| Non Family Households | 2,738 | 4,992 | 43,255,233 |
| Single householder, w/children | 9.0% | 22.2% | 15.8% |
| Single householder, no children | 6.4% | 10.9% | 10.8% |