| | Washington, PA | Slidell, LA | United States |
| Population | 13,322 | 28,537 | 329,725,481 |
| Female Population | 49.9% | 53.7% | 50.5% |
| Male Population | 50.2% | 46.3% | 49.5% |
| Median Age | 36.5 | 38 | 38.4 |
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| Population - 2010 | 14,026 | 27,342 | 309,327,143 |
| Population - 2000 | 15,268 | 25,695 | 285,036,114 |
| Population - 1990 | 15,864 | 24,124 | 251,960,433 |
| Pop. 2000 to Now | -13.2% | 7.2% | 15.6% |
| Pop. 1990 to Now | -16.5% | 14.2% | 30.8% |
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| Population Density | 4,519.0 | 1,861.5 | 93.4 |
| Land Area | 2.9 | 15.3 | 3,531,905.4 |
| Water Area | 0.0 | 0.4 | 264,836.8 |
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| Est. Total Population By Age | | | |
| | Washington, PA | Slidell, LA | United States |
| Age 0 to 4 | 6.3% | 5.6% | 5.9% |
| Age 5 to 9 | 4.7% | 8.1% | 6.1% |
| Age 10 to 14 | 3.4% | 7.8% | 6.6% |
| Age 15 to 17 | 2.5% | 4.1% | 3.9% |
| Age 18 to 20 | 9.3% | 2.9% | 4.0% |
| Age 21 to 24 | 7.3% | 4.4% | 5.2% |
| Age 25 to 34 | 14.4% | 12.4% | 13.8% |
| Age 35 to 44 | 9.8% | 14.7% | 12.9% |
| Age 45 to 54 | 13.6% | 10.0% | 12.6% |
| Age 55 to 59 | 8.6% | 5.4% | 6.7% |
| Age 60 to 64 | 5.2% | 6.1% | 6.3% |
| Age 65 to 74 | 9.8% | 11.4% | 9.6% |
| Age 75 to 84 | 3.8% | 4.5% | 4.5% |
| Age 85 and over | 1.3% | 2.6% | 1.9% |
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| Race | | | |
| | Washington, PA | Slidell, LA | United States |
| White | 72.7% | 69.1% | 59.4% |
| Black | 14.6% | 17.4% | 12.2% |
| Asian | 1.8% | 2.3% | 5.6% |
| Native American | 0.0% | 0.4% | 0.6% |
| Hawaiian, Pacific Islander | 0.0% | 0.0% | 0.2% |
| Other | 0.2% | 0.2% | 0.4% |
| Two or More Races | 6.4% | 4.9% | 3.2% |
| Hispanic | 4.3% | 5.6% | 18.4% |
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| Marriage & Family | | | |
| | Washington, PA | Slidell, LA | United States |
| Married Population | 29.4% | 46.2% | 49.8% |
| Currently Married | 28.1% | 43.5% | 48.0% |
| Married but Separated | 1.3% | 2.7% | 1.8% |
| Single Population | 70.6% | 53.8% | 50.2% |
| Never Married | 48.0% | 29.6% | 33.8% |
| Divorced | 15.9% | 15.8% | 10.8% |
| Widowed | 6.7% | 8.4% | 5.6% |
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| Household Size | 2.04 | 2.64 | 2.60 |
| Households | 5,667 | 10,680 | 124,010,992 |
| Family Households | 2,665 | 7,116 | 80,755,759 |
| Married couple, w/children | 18.3% | 25.2% | 30.5% |
| Married couple, no children | 37.1% | 36.4% | 42.9% |
| Non Family Households | 3,002 | 3,564 | 43,255,233 |
| Single householder, w/children | 24.2% | 25.5% | 15.8% |
| Single householder, no children | 20.4% | 12.8% | 10.8% |