| | Willimantic, CT | Buffalo, NY | United States |
| Population | 18,150 | 276,011 | 329,725,481 |
| Female Population | 52.0% | 51.9% | 50.5% |
| Male Population | 48.0% | 48.1% | 49.5% |
| Median Age | 29.7 | 33.9 | 38.4 |
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| Population - 2010 | 17,485 | 261,280 | 309,327,143 |
| Population - 2000 | 15,823 | 292,648 | 285,036,114 |
| Population - 1990 | 14,966 | 328,123 | 251,960,433 |
| Pop. 2000 to Now | 10.9% | -13.0% | 15.6% |
| Pop. 1990 to Now | 17.3% | -22.4% | 30.8% |
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| Population Density | 4,126.9 | 6,835.7 | 93.4 |
| Land Area | 4.4 | 40.4 | 3,531,905.4 |
| Water Area | 0.1 | 12.1 | 264,836.8 |
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| Est. Total Population By Age | | | |
| | Willimantic, CT | Buffalo, NY | United States |
| Age 0 to 4 | 2.2% | 6.4% | 5.9% |
| Age 5 to 9 | 5.5% | 6.4% | 6.1% |
| Age 10 to 14 | 5.8% | 6.0% | 6.6% |
| Age 15 to 17 | 4.0% | 3.7% | 3.9% |
| Age 18 to 20 | 16.2% | 4.8% | 4.0% |
| Age 21 to 24 | 10.2% | 6.5% | 5.2% |
| Age 25 to 34 | 12.8% | 17.9% | 13.8% |
| Age 35 to 44 | 12.6% | 12.0% | 12.9% |
| Age 45 to 54 | 8.9% | 10.9% | 12.6% |
| Age 55 to 59 | 6.0% | 6.2% | 6.7% |
| Age 60 to 64 | 4.6% | 6.2% | 6.3% |
| Age 65 to 74 | 5.9% | 8.1% | 9.6% |
| Age 75 to 84 | 3.1% | 3.3% | 4.5% |
| Age 85 and over | 2.1% | 1.6% | 1.9% |
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| Race | | | |
| | Willimantic, CT | Buffalo, NY | United States |
| White | 44.0% | 44.7% | 59.4% |
| Black | 5.2% | 32.3% | 12.2% |
| Asian | 1.9% | 6.7% | 5.6% |
| Native American | 0.1% | 0.3% | 0.6% |
| Hawaiian, Pacific Islander | 0.0% | 0.0% | 0.2% |
| Other | 0.3% | 0.3% | 0.4% |
| Two or More Races | 1.9% | 3.5% | 3.2% |
| Hispanic | 46.6% | 12.2% | 18.4% |
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| Marriage & Family | | | |
| | Willimantic, CT | Buffalo, NY | United States |
| Married Population | 24.0% | 32.0% | 49.8% |
| Currently Married | 22.7% | 29.5% | 48.0% |
| Married but Separated | 1.3% | 2.6% | 1.8% |
| Single Population | 76.0% | 68.0% | 50.2% |
| Never Married | 62.2% | 51.2% | 33.8% |
| Divorced | 10.2% | 11.2% | 10.8% |
| Widowed | 3.6% | 5.6% | 5.6% |
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| Household Size | 2.40 | 2.26 | 2.60 |
| Households | 6,198 | 118,071 | 124,010,992 |
| Family Households | 3,185 | 58,775 | 80,755,759 |
| Married couple, w/children | 17.7% | 21.6% | 30.5% |
| Married couple, no children | 28.6% | 28.6% | 42.9% |
| Non Family Households | 3,013 | 59,296 | 43,255,233 |
| Single householder, w/children | 39.2% | 30.5% | 15.8% |
| Single householder, no children | 14.4% | 19.3% | 10.8% |