| | Killingworth, CT | Durham, CT | United States |
| Population | 6,276 | 7,242 | 329,725,481 |
| Female Population | 52.1% | 48.4% | 50.5% |
| Male Population | 47.9% | 51.6% | 49.5% |
| Median Age | 50.6 | 46.1 | 38.4 |
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| Population - 2010 | 6,519 | 7,386 | 309,327,143 |
| Population - 2000 | 6,018 | 6,627 | 285,036,114 |
| Population - 1990 | 4,814 | 5,732 | 251,960,433 |
| Pop. 2000 to Now | 5.4% | 7.7% | 15.6% |
| Pop. 1990 to Now | 31.7% | 24.5% | 30.8% |
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| Population Density | 177.6 | 306.1 | 93.4 |
| Land Area | 35.3 | 23.7 | 3,531,905.4 |
| Water Area | 0.5 | 0.2 | 264,836.8 |
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| Est. Total Population By Age | | | |
| | Killingworth, CT | Durham, CT | United States |
| Age 0 to 4 | 4.8% | 5.6% | 5.9% |
| Age 5 to 9 | 6.2% | 3.9% | 6.1% |
| Age 10 to 14 | 4.6% | 5.3% | 6.6% |
| Age 15 to 17 | 2.9% | 3.9% | 3.9% |
| Age 18 to 20 | 2.5% | 2.7% | 4.0% |
| Age 21 to 24 | 4.1% | 2.7% | 5.2% |
| Age 25 to 34 | 8.3% | 10.3% | 13.8% |
| Age 35 to 44 | 8.5% | 13.2% | 12.9% |
| Age 45 to 54 | 16.3% | 17.2% | 12.6% |
| Age 55 to 59 | 10.2% | 8.0% | 6.7% |
| Age 60 to 64 | 9.2% | 8.2% | 6.3% |
| Age 65 to 74 | 12.8% | 12.9% | 9.6% |
| Age 75 to 84 | 7.3% | 4.3% | 4.5% |
| Age 85 and over | 2.3% | 1.8% | 1.9% |
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| Race | | | |
| | Killingworth, CT | Durham, CT | United States |
| White | 91.3% | 92.4% | 59.4% |
| Black | 0.0% | 0.1% | 12.2% |
| Asian | 1.5% | 1.0% | 5.6% |
| Native American | 0.0% | 0.0% | 0.6% |
| Hawaiian, Pacific Islander | 0.0% | 0.0% | 0.2% |
| Other | 0.5% | 0.0% | 0.4% |
| Two or More Races | 4.4% | 3.5% | 3.2% |
| Hispanic | 2.3% | 2.9% | 18.4% |
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| Marriage & Family | | | |
| | Killingworth, CT | Durham, CT | United States |
| Married Population | 62.9% | 60.0% | 49.8% |
| Currently Married | 62.9% | 59.6% | 48.0% |
| Married but Separated | 0.0% | 0.4% | 1.8% |
| Single Population | 37.1% | 40.0% | 50.2% |
| Never Married | 23.9% | 25.5% | 33.8% |
| Divorced | 6.4% | 9.2% | 10.8% |
| Widowed | 6.8% | 5.3% | 5.6% |
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| Household Size | 2.76 | 2.38 | 2.60 |
| Households | 2,276 | 3,019 | 124,010,992 |
| Family Households | 1,742 | 2,204 | 80,755,759 |
| Married couple, w/children | 32.9% | 40.0% | 30.5% |
| Married couple, no children | 58.9% | 49.3% | 42.9% |
| Non Family Households | 534 | 815 | 43,255,233 |
| Single householder, w/children | 3.8% | 5.3% | 15.8% |
| Single householder, no children | 4.4% | 5.4% | 10.8% |