| | Groton, CT | Amherst, NY | United States |
| Population | 38,686 | 128,783 | 329,725,481 |
| Female Population | 44.7% | 51.6% | 50.5% |
| Male Population | 55.3% | 48.4% | 49.5% |
| Median Age | 34.2 | 39.4 | 38.4 |
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| Population - 2010 | 40,094 | 122,363 | 309,327,143 |
| Population - 2000 | 39,907 | 116,510 | 285,036,114 |
| Population - 1990 | 45,144 | 111,711 | 251,960,433 |
| Pop. 2000 to Now | -4.1% | 8.1% | 15.6% |
| Pop. 1990 to Now | -15.3% | 12.8% | 30.8% |
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| Population Density | 1,246.7 | 2,420.9 | 93.4 |
| Land Area | 31.0 | 53.2 | 3,531,905.4 |
| Water Area | 14.3 | 0.4 | 264,836.8 |
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| Est. Total Population By Age | | | |
| | Groton, CT | Amherst, NY | United States |
| Age 0 to 4 | 6.0% | 5.1% | 5.9% |
| Age 5 to 9 | 4.4% | 5.1% | 6.1% |
| Age 10 to 14 | 5.6% | 5.9% | 6.6% |
| Age 15 to 17 | 3.0% | 3.8% | 3.9% |
| Age 18 to 20 | 5.6% | 6.6% | 4.0% |
| Age 21 to 24 | 9.3% | 6.2% | 5.2% |
| Age 25 to 34 | 17.3% | 11.4% | 13.8% |
| Age 35 to 44 | 10.0% | 11.9% | 12.9% |
| Age 45 to 54 | 10.4% | 11.0% | 12.6% |
| Age 55 to 59 | 5.9% | 6.6% | 6.7% |
| Age 60 to 64 | 5.5% | 5.6% | 6.3% |
| Age 65 to 74 | 8.9% | 11.3% | 9.6% |
| Age 75 to 84 | 4.9% | 5.7% | 4.5% |
| Age 85 and over | 3.3% | 3.7% | 1.9% |
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| Race | | | |
| | Groton, CT | Amherst, NY | United States |
| White | 67.0% | 76.7% | 59.4% |
| Black | 5.9% | 5.5% | 12.2% |
| Asian | 7.0% | 9.7% | 5.6% |
| Native American | 0.4% | 0.3% | 0.6% |
| Hawaiian, Pacific Islander | 0.0% | 0.0% | 0.2% |
| Other | 0.3% | 0.1% | 0.4% |
| Two or More Races | 6.2% | 3.1% | 3.2% |
| Hispanic | 13.1% | 4.5% | 18.4% |
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| Marriage & Family | | | |
| | Groton, CT | Amherst, NY | United States |
| Married Population | 46.3% | 49.0% | 49.8% |
| Currently Married | 45.9% | 48.1% | 48.0% |
| Married but Separated | 0.4% | 0.9% | 1.8% |
| Single Population | 53.7% | 51.0% | 50.2% |
| Never Married | 37.2% | 35.5% | 33.8% |
| Divorced | 11.6% | 9.2% | 10.8% |
| Widowed | 5.0% | 6.4% | 5.6% |
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| Household Size | 2.23 | 2.33 | 2.60 |
| Households | 16,043 | 51,766 | 124,010,992 |
| Family Households | 9,685 | 31,132 | 80,755,759 |
| Married couple, w/children | 27.4% | 32.4% | 30.5% |
| Married couple, no children | 42.6% | 47.0% | 42.9% |
| Non Family Households | 6,358 | 20,634 | 43,255,233 |
| Single householder, w/children | 18.2% | 10.9% | 15.8% |
| Single householder, no children | 11.8% | 9.7% | 10.8% |