| | Grantham, NH | Newmarket, NH | United States |
| Population | 3,366 | 9,365 | 329,725,481 |
| Female Population | 53.1% | 48.4% | 50.5% |
| Male Population | 46.9% | 51.7% | 49.5% |
| Median Age | 50.1 | 40.1 | 38.4 |
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| Population - 2010 | 2,976 | 8,974 | 309,327,143 |
| Population - 2000 | 2,167 | 8,027 | 285,036,114 |
| Population - 1990 | 1,247 | 7,157 | 251,960,433 |
| Pop. 2000 to Now | 36.4% | 14.7% | 15.6% |
| Pop. 1990 to Now | 137.0% | 28.6% | 30.8% |
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| Population Density | 123.9 | 746.5 | 93.4 |
| Land Area | 27.2 | 12.5 | 3,531,905.4 |
| Water Area | 0.9 | 1.6 | 264,836.8 |
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| Est. Total Population By Age | | | |
| | Grantham, NH | Newmarket, NH | United States |
| Age 0 to 4 | 0.0% | 4.0% | 5.9% |
| Age 5 to 9 | 8.5% | 4.8% | 6.1% |
| Age 10 to 14 | 9.4% | 5.0% | 6.6% |
| Age 15 to 17 | 5.3% | 1.6% | 3.9% |
| Age 18 to 20 | 4.5% | 1.4% | 4.0% |
| Age 21 to 24 | 2.4% | 6.1% | 5.2% |
| Age 25 to 34 | 1.4% | 19.3% | 13.8% |
| Age 35 to 44 | 13.3% | 14.6% | 12.9% |
| Age 45 to 54 | 14.5% | 12.3% | 12.6% |
| Age 55 to 59 | 13.8% | 5.7% | 6.7% |
| Age 60 to 64 | 6.1% | 8.9% | 6.3% |
| Age 65 to 74 | 11.5% | 9.8% | 9.6% |
| Age 75 to 84 | 7.8% | 5.6% | 4.5% |
| Age 85 and over | 1.5% | 0.9% | 1.9% |
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| Race | | | |
| | Grantham, NH | Newmarket, NH | United States |
| White | 99.2% | 92.7% | 59.4% |
| Black | 0.0% | 1.2% | 12.2% |
| Asian | 0.0% | 2.3% | 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 | 0.0% | 2.4% | 3.2% |
| Hispanic | 0.8% | 1.5% | 18.4% |
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| Marriage & Family | | | |
| | Grantham, NH | Newmarket, NH | United States |
| Married Population | 70.7% | 51.0% | 49.8% |
| Currently Married | 67.0% | 50.1% | 48.0% |
| Married but Separated | 3.7% | 0.9% | 1.8% |
| Single Population | 29.3% | 49.0% | 50.2% |
| Never Married | 17.9% | 33.0% | 33.8% |
| Divorced | 4.0% | 12.2% | 10.8% |
| Widowed | 7.4% | 3.9% | 5.6% |
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| Household Size | 2.75 | 2.17 | 2.60 |
| Households | 1,224 | 4,322 | 124,010,992 |
| Family Households | 1,024 | 2,319 | 80,755,759 |
| Married couple, w/children | 34.4% | 24.5% | 30.5% |
| Married couple, no children | 58.0% | 57.8% | 42.9% |
| Non Family Households | 200 | 2,003 | 43,255,233 |
| Single householder, w/children | 4.1% | 11.6% | 15.8% |
| Single householder, no children | 3.5% | 6.1% | 10.8% |