| | Mount Union, PA | Williamsburg, PA | United States |
| Population | 2,093 | 1,161 | 329,725,481 |
| Female Population | 48.4% | 49.8% | 50.5% |
| Male Population | 51.7% | 50.2% | 49.5% |
| Median Age | 35.5 | 36.5 | 38.4 |
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| Population - 2010 | 2,446 | 1,248 | 309,327,143 |
| Population - 2000 | 2,504 | 1,345 | 285,036,114 |
| Population - 1990 | 2,878 | 1,456 | 251,960,433 |
| Pop. 2000 to Now | -7.7% | -13.2% | 15.6% |
| Pop. 1990 to Now | -19.7% | -19.9% | 30.8% |
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| Population Density | 1,804.3 | 3,172.1 | 93.4 |
| Land Area | 1.2 | 0.4 | 3,531,905.4 |
| Water Area | 0.1 | 0.0 | 264,836.8 |
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| Est. Total Population By Age | | | |
| | Mount Union, PA | Williamsburg, PA | United States |
| Age 0 to 4 | 9.1% | 8.4% | 5.9% |
| Age 5 to 9 | 5.6% | 6.8% | 6.1% |
| Age 10 to 14 | 5.3% | 8.1% | 6.6% |
| Age 15 to 17 | 4.9% | 2.3% | 3.9% |
| Age 18 to 20 | 2.5% | 3.0% | 4.0% |
| Age 21 to 24 | 6.8% | 5.6% | 5.2% |
| Age 25 to 34 | 15.2% | 13.0% | 13.8% |
| Age 35 to 44 | 7.6% | 12.1% | 12.9% |
| Age 45 to 54 | 12.6% | 12.0% | 12.6% |
| Age 55 to 59 | 8.8% | 4.8% | 6.7% |
| Age 60 to 64 | 4.3% | 4.5% | 6.3% |
| Age 65 to 74 | 10.3% | 12.1% | 9.6% |
| Age 75 to 84 | 4.2% | 5.9% | 4.5% |
| Age 85 and over | 2.9% | 1.4% | 1.9% |
| space1 | | | |
| Race | | | |
| | Mount Union, PA | Williamsburg, PA | United States |
| White | 87.1% | 92.3% | 59.4% |
| Black | 6.8% | 0.0% | 12.2% |
| Asian | 0.0% | 0.6% | 5.6% |
| Native American | 0.0% | 0.0% | 0.6% |
| Hawaiian, Pacific Islander | 0.0% | 0.0% | 0.2% |
| Other | 0.0% | 0.0% | 0.4% |
| Two or More Races | 4.5% | 5.9% | 3.2% |
| Hispanic | 1.6% | 1.2% | 18.4% |
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| Marriage & Family | | | |
| | Mount Union, PA | Williamsburg, PA | United States |
| Married Population | 42.3% | 49.3% | 49.8% |
| Currently Married | 39.3% | 48.0% | 48.0% |
| Married but Separated | 2.9% | 1.2% | 1.8% |
| Single Population | 57.7% | 50.7% | 50.2% |
| Never Married | 40.2% | 31.1% | 33.8% |
| Divorced | 12.1% | 12.8% | 10.8% |
| Widowed | 5.4% | 6.8% | 5.6% |
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| Household Size | 2.37 | 2.46 | 2.60 |
| Households | 871 | 472 | 124,010,992 |
| Family Households | 526 | 288 | 80,755,759 |
| Married couple, w/children | 23.6% | 30.9% | 30.5% |
| Married couple, no children | 35.7% | 39.6% | 42.9% |
| Non Family Households | 345 | 184 | 43,255,233 |
| Single householder, w/children | 30.0% | 19.4% | 15.8% |
| Single householder, no children | 10.6% | 10.1% | 10.8% |