| | Tredyffrin, PA | Willistown, PA | United States |
| Population | 31,596 | 11,184 | 329,725,481 |
| Female Population | 50.2% | 49.1% | 50.5% |
| Male Population | 49.8% | 50.9% | 49.5% |
| Median Age | 42.5 | 50 | 38.4 |
| space3 | | | |
| Population - 2010 | 29,356 | 10,513 | 309,327,143 |
| Population - 2000 | 29,062 | 10,011 | 285,036,114 |
| Population - 1990 | 28,028 | 9,380 | 251,960,433 |
| Pop. 2000 to Now | 0.6% | 9.7% | 15.6% |
| Pop. 1990 to Now | 4.3% | 17.1% | 30.8% |
| space4 | | | |
| Population Density | 1,598.6 | 617.6 | 93.4 |
| Land Area | 19.8 | 18.1 | 3,531,905.4 |
| Water Area | 0.1 | 0.2 | 264,836.8 |
| space | | | |
| Est. Total Population By Age | | | |
| | Tredyffrin, PA | Willistown, PA | United States |
| Age 0 to 4 | 5.1% | 5.7% | 5.9% |
| Age 5 to 9 | 6.9% | 4.3% | 6.1% |
| Age 10 to 14 | 8.3% | 6.9% | 6.6% |
| Age 15 to 17 | 5.1% | 3.1% | 3.9% |
| Age 18 to 20 | 1.9% | 2.1% | 4.0% |
| Age 21 to 24 | 3.2% | 2.9% | 5.2% |
| Age 25 to 34 | 9.5% | 9.1% | 13.8% |
| Age 35 to 44 | 14.3% | 10.6% | 12.9% |
| Age 45 to 54 | 14.2% | 13.6% | 12.6% |
| Age 55 to 59 | 8.4% | 8.6% | 6.7% |
| Age 60 to 64 | 5.7% | 8.6% | 6.3% |
| Age 65 to 74 | 9.7% | 14.5% | 9.6% |
| Age 75 to 84 | 5.1% | 6.2% | 4.5% |
| Age 85 and over | 2.4% | 3.7% | 1.9% |
| space1 | | | |
| Race | | | |
| | Tredyffrin, PA | Willistown, PA | United States |
| White | 73.6% | 87.8% | 59.4% |
| Black | 2.0% | 2.3% | 12.2% |
| Asian | 18.4% | 7.7% | 5.6% |
| Native American | 0.0% | 0.0% | 0.6% |
| Hawaiian, Pacific Islander | 0.0% | 0.0% | 0.2% |
| Other | 0.2% | 0.0% | 0.4% |
| Two or More Races | 3.1% | 1.4% | 3.2% |
| Hispanic | 2.8% | 0.9% | 18.4% |
| space2 | | | |
| Marriage & Family | | | |
| | Tredyffrin, PA | Willistown, PA | United States |
| Married Population | 63.9% | 66.4% | 49.8% |
| Currently Married | 63.1% | 65.3% | 48.0% |
| Married but Separated | 0.8% | 1.1% | 1.8% |
| Single Population | 36.1% | 33.6% | 50.2% |
| Never Married | 24.7% | 20.3% | 33.8% |
| Divorced | 7.2% | 8.5% | 10.8% |
| Widowed | 4.2% | 4.8% | 5.6% |
| space5 | | | |
| Household Size | 2.63 | 2.54 | 2.60 |
| Households | 11,972 | 4,313 | 124,010,992 |
| Family Households | 8,201 | 3,239 | 80,755,759 |
| Married couple, w/children | 48.5% | 31.0% | 30.5% |
| Married couple, no children | 43.5% | 57.8% | 42.9% |
| Non Family Households | 3,771 | 1,074 | 43,255,233 |
| Single householder, w/children | 4.6% | 7.2% | 15.8% |
| Single householder, no children | 3.4% | 4.0% | 10.8% |