| | Seneca, PA | Lewes, DE | United States |
| Population | 883 | 3,257 | 329,725,481 |
| Female Population | 48.3% | 49.1% | 50.5% |
| Male Population | 51.8% | 50.9% | 49.5% |
| Median Age | 53.2 | 65.7 | 38.4 |
| space3 | | | |
| Population - 2010 | 1,051 | 2,858 | 309,327,143 |
| Population - 2000 | 966 | 2,932 | 285,036,114 |
| Population - 1990 | 1,029 | 2,295 | 251,960,433 |
| Pop. 2000 to Now | 20.0% | 16.5% | 15.6% |
| Pop. 1990 to Now | 12.6% | 48.9% | 30.8% |
| space4 | | | |
| Population Density | 392.8 | 842.7 | 93.4 |
| Land Area | 2.2 | 3.9 | 3,531,905.4 |
| Water Area | 0.0 | 0.9 | 264,836.8 |
| space | | | |
| Est. Total Population By Age | | | |
| | Seneca, PA | Lewes, DE | United States |
| Age 0 to 4 | 3.7% | 0.5% | 5.9% |
| Age 5 to 9 | 0.8% | 1.6% | 6.1% |
| Age 10 to 14 | 9.3% | 3.3% | 6.6% |
| Age 15 to 17 | 8.9% | 0.1% | 3.9% |
| Age 18 to 20 | 2.4% | 0.0% | 4.0% |
| Age 21 to 24 | 0.0% | 2.1% | 5.2% |
| Age 25 to 34 | 2.5% | 8.8% | 13.8% |
| Age 35 to 44 | 13.4% | 6.0% | 12.9% |
| Age 45 to 54 | 11.3% | 3.5% | 12.6% |
| Age 55 to 59 | 4.3% | 7.5% | 6.7% |
| Age 60 to 64 | 12.0% | 13.1% | 6.3% |
| Age 65 to 74 | 21.1% | 32.3% | 9.6% |
| Age 75 to 84 | 6.8% | 16.8% | 4.5% |
| Age 85 and over | 3.5% | 4.4% | 1.9% |
| space1 | | | |
| Race | | | |
| | Seneca, PA | Lewes, DE | United States |
| White | 96.8% | 96.1% | 59.4% |
| Black | 0.0% | 1.0% | 12.2% |
| Asian | 1.4% | 0.0% | 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 | 1.8% | 1.3% | 3.2% |
| Hispanic | 0.0% | 1.5% | 18.4% |
| space2 | | | |
| Marriage & Family | | | |
| | Seneca, PA | Lewes, DE | United States |
| Married Population | 62.3% | 62.2% | 49.8% |
| Currently Married | 62.3% | 61.9% | 48.0% |
| Married but Separated | 0.0% | 0.3% | 1.8% |
| Single Population | 37.7% | 37.8% | 50.2% |
| Never Married | 20.2% | 19.4% | 33.8% |
| Divorced | 11.3% | 8.7% | 10.8% |
| Widowed | 6.2% | 9.6% | 5.6% |
| space5 | | | |
| Household Size | 2.13 | 2.00 | 2.60 |
| Households | 415 | 1,546 | 124,010,992 |
| Family Households | 290 | 1,040 | 80,755,759 |
| Married couple, w/children | 28.6% | 9.4% | 30.5% |
| Married couple, no children | 53.1% | 81.7% | 42.9% |
| Non Family Households | 125 | 506 | 43,255,233 |
| Single householder, w/children | 15.9% | 0.0% | 15.8% |
| Single householder, no children | 2.4% | 8.8% | 10.8% |