| | Marlborough, CT | Old Saybrook, CT | United States |
| Population | 6,155 | 10,506 | 329,725,481 |
| Female Population | 50.4% | 56.2% | 50.5% |
| Male Population | 49.6% | 43.8% | 49.5% |
| Median Age | 43.2 | 56.1 | 38.4 |
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| Population - 2010 | 6,390 | 10,238 | 309,327,143 |
| Population - 2000 | 5,709 | 10,367 | 285,036,114 |
| Population - 1990 | 5,535 | 9,552 | 251,960,433 |
| Pop. 2000 to Now | 10.4% | -3.3% | 15.6% |
| Pop. 1990 to Now | 13.9% | 5.0% | 30.8% |
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| Population Density | 263.6 | 697.7 | 93.4 |
| Land Area | 23.4 | 15.1 | 3,531,905.4 |
| Water Area | 0.2 | 6.5 | 264,836.8 |
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| Est. Total Population By Age | | | |
| | Marlborough, CT | Old Saybrook, CT | United States |
| Age 0 to 4 | 4.3% | 2.6% | 5.9% |
| Age 5 to 9 | 4.1% | 3.3% | 6.1% |
| Age 10 to 14 | 6.9% | 4.7% | 6.6% |
| Age 15 to 17 | 8.2% | 4.9% | 3.9% |
| Age 18 to 20 | 2.0% | 2.5% | 4.0% |
| Age 21 to 24 | 4.6% | 2.9% | 5.2% |
| Age 25 to 34 | 10.6% | 7.6% | 13.8% |
| Age 35 to 44 | 11.9% | 7.5% | 12.9% |
| Age 45 to 54 | 16.8% | 11.6% | 12.6% |
| Age 55 to 59 | 8.6% | 10.1% | 6.7% |
| Age 60 to 64 | 6.3% | 14.5% | 6.3% |
| Age 65 to 74 | 10.2% | 12.9% | 9.6% |
| Age 75 to 84 | 3.7% | 10.9% | 4.5% |
| Age 85 and over | 1.9% | 4.1% | 1.9% |
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| Race | | | |
| | Marlborough, CT | Old Saybrook, CT | United States |
| White | 87.4% | 93.0% | 59.4% |
| Black | 2.3% | 0.5% | 12.2% |
| Asian | 1.6% | 1.5% | 5.6% |
| Native American | 0.0% | 0.0% | 0.6% |
| Hawaiian, Pacific Islander | 0.0% | 0.0% | 0.2% |
| Other | 0.2% | 0.0% | 0.4% |
| Two or More Races | 0.4% | 0.4% | 3.2% |
| Hispanic | 8.1% | 4.5% | 18.4% |
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| Marriage & Family | | | |
| | Marlborough, CT | Old Saybrook, CT | United States |
| Married Population | 60.6% | 54.4% | 49.8% |
| Currently Married | 60.4% | 53.6% | 48.0% |
| Married but Separated | 0.2% | 0.9% | 1.8% |
| Single Population | 39.4% | 45.6% | 50.2% |
| Never Married | 27.7% | 22.7% | 33.8% |
| Divorced | 7.6% | 15.1% | 10.8% |
| Widowed | 4.2% | 7.8% | 5.6% |
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| Household Size | 2.82 | 2.27 | 2.60 |
| Households | 2,142 | 4,584 | 124,010,992 |
| Family Households | 1,821 | 2,677 | 80,755,759 |
| Married couple, w/children | 39.2% | 21.6% | 30.5% |
| Married couple, no children | 44.6% | 65.6% | 42.9% |
| Non Family Households | 321 | 1,907 | 43,255,233 |
| Single householder, w/children | 10.7% | 9.9% | 15.8% |
| Single householder, no children | 5.5% | 3.0% | 10.8% |