| | Irwin, PA | Knoxville, TN | United States |
| Population | 3,894 | 189,339 | 329,725,481 |
| Female Population | 54.1% | 51.7% | 50.5% |
| Male Population | 45.9% | 48.3% | 49.5% |
| Median Age | 45.3 | 33.5 | 38.4 |
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| Population - 2010 | 3,988 | 178,269 | 309,327,143 |
| Population - 2000 | 4,366 | 173,890 | 285,036,114 |
| Population - 1990 | 4,604 | 165,121 | 251,960,433 |
| Pop. 2000 to Now | -14.9% | 9.4% | 15.6% |
| Pop. 1990 to Now | -19.3% | 15.2% | 30.8% |
| space4 | | | |
| Population Density | 4,652.3 | 1,918.1 | 93.4 |
| Land Area | 0.8 | 98.7 | 3,531,905.4 |
| Water Area | 0.0 | 5.5 | 264,836.8 |
| space | | | |
| Est. Total Population By Age | | | |
| | Irwin, PA | Knoxville, TN | United States |
| Age 0 to 4 | 4.9% | 5.3% | 5.9% |
| Age 5 to 9 | 5.3% | 5.5% | 6.1% |
| Age 10 to 14 | 3.6% | 4.9% | 6.6% |
| Age 15 to 17 | 4.9% | 3.2% | 3.9% |
| Age 18 to 20 | 1.2% | 7.1% | 4.0% |
| Age 21 to 24 | 3.0% | 9.9% | 5.2% |
| Age 25 to 34 | 11.7% | 15.9% | 13.8% |
| Age 35 to 44 | 15.2% | 11.9% | 12.9% |
| Age 45 to 54 | 9.9% | 11.1% | 12.6% |
| Age 55 to 59 | 15.0% | 6.0% | 6.7% |
| Age 60 to 64 | 7.6% | 5.2% | 6.3% |
| Age 65 to 74 | 11.2% | 8.3% | 9.6% |
| Age 75 to 84 | 4.5% | 3.9% | 4.5% |
| Age 85 and over | 2.0% | 1.7% | 1.9% |
| space1 | | | |
| Race | | | |
| | Irwin, PA | Knoxville, TN | United States |
| White | 93.8% | 72.1% | 59.4% |
| Black | 0.8% | 16.3% | 12.2% |
| Asian | 0.0% | 1.7% | 5.6% |
| Native American | 0.0% | 0.1% | 0.6% |
| Hawaiian, Pacific Islander | 0.0% | 0.0% | 0.2% |
| Other | 0.0% | 0.4% | 0.4% |
| Two or More Races | 3.1% | 3.8% | 3.2% |
| Hispanic | 2.2% | 5.7% | 18.4% |
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| Marriage & Family | | | |
| | Irwin, PA | Knoxville, TN | United States |
| Married Population | 41.7% | 36.7% | 49.8% |
| Currently Married | 39.8% | 34.5% | 48.0% |
| Married but Separated | 2.0% | 2.2% | 1.8% |
| Single Population | 58.3% | 63.3% | 50.2% |
| Never Married | 29.8% | 43.4% | 33.8% |
| Divorced | 21.4% | 13.8% | 10.8% |
| Widowed | 7.0% | 6.1% | 5.6% |
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| Household Size | 1.88 | 2.19 | 2.60 |
| Households | 2,066 | 82,586 | 124,010,992 |
| Family Households | 929 | 39,549 | 80,755,759 |
| Married couple, w/children | 21.5% | 25.1% | 30.5% |
| Married couple, no children | 49.5% | 38.6% | 42.9% |
| Non Family Households | 1,137 | 43,037 | 43,255,233 |
| Single householder, w/children | 25.2% | 23.9% | 15.8% |
| Single householder, no children | 3.8% | 12.5% | 10.8% |