| | Willow Street, PA | Quarryville, PA | United States |
| Population | 9,338 | 2,830 | 329,725,481 |
| Female Population | 53.8% | 47.9% | 50.5% |
| Male Population | 46.2% | 52.1% | 49.5% |
| Median Age | 54.3 | 33.5 | 38.4 |
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| Population - 2010 | 7,354 | 2,611 | 309,327,143 |
| Population - 2000 | 7,258 | 1,994 | 285,036,114 |
| Population - 1990 | 5,817 | 1,642 | 251,960,433 |
| Pop. 2000 to Now | 19.0% | 37.7% | 15.6% |
| Pop. 1990 to Now | 48.4% | 67.2% | 30.8% |
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| Population Density | 1,718.4 | 2,192.1 | 93.4 |
| Land Area | 5.4 | 1.3 | 3,531,905.4 |
| Water Area | 0.0 | 0.0 | 264,836.8 |
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| Est. Total Population By Age | | | |
| | Willow Street, PA | Quarryville, PA | United States |
| Age 0 to 4 | 2.8% | 9.2% | 5.9% |
| Age 5 to 9 | 2.8% | 8.1% | 6.1% |
| Age 10 to 14 | 4.6% | 9.0% | 6.6% |
| Age 15 to 17 | 7.0% | 3.1% | 3.9% |
| Age 18 to 20 | 1.7% | 4.7% | 4.0% |
| Age 21 to 24 | 5.3% | 2.2% | 5.2% |
| Age 25 to 34 | 8.3% | 16.6% | 13.8% |
| Age 35 to 44 | 7.5% | 10.0% | 12.9% |
| Age 45 to 54 | 11.1% | 7.7% | 12.6% |
| Age 55 to 59 | 5.9% | 6.8% | 6.7% |
| Age 60 to 64 | 4.5% | 7.7% | 6.3% |
| Age 65 to 74 | 13.7% | 9.7% | 9.6% |
| Age 75 to 84 | 16.2% | 4.9% | 4.5% |
| Age 85 and over | 8.6% | 0.5% | 1.9% |
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| Race | | | |
| | Willow Street, PA | Quarryville, PA | United States |
| White | 84.8% | 80.0% | 59.4% |
| Black | 0.9% | 2.0% | 12.2% |
| Asian | 3.8% | 6.6% | 5.6% |
| Native American | 0.2% | 0.0% | 0.6% |
| Hawaiian, Pacific Islander | 0.0% | 0.0% | 0.2% |
| Other | 1.3% | 0.0% | 0.4% |
| Two or More Races | 1.6% | 0.8% | 3.2% |
| Hispanic | 7.4% | 10.5% | 18.4% |
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| Marriage & Family | | | |
| | Willow Street, PA | Quarryville, PA | United States |
| Married Population | 62.5% | 58.7% | 49.8% |
| Currently Married | 59.7% | 57.2% | 48.0% |
| Married but Separated | 2.8% | 1.5% | 1.8% |
| Single Population | 37.5% | 41.3% | 50.2% |
| Never Married | 21.7% | 26.8% | 33.8% |
| Divorced | 6.5% | 8.9% | 10.8% |
| Widowed | 9.4% | 5.6% | 5.6% |
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| Household Size | 2.29 | 2.75 | 2.60 |
| Households | 3,951 | 1,029 | 124,010,992 |
| Family Households | 2,666 | 767 | 80,755,759 |
| Married couple, w/children | 26.9% | 28.0% | 30.5% |
| Married couple, no children | 63.1% | 44.9% | 42.9% |
| Non Family Households | 1,285 | 262 | 43,255,233 |
| Single householder, w/children | 4.2% | 16.7% | 15.8% |
| Single householder, no children | 5.7% | 10.4% | 10.8% |