| | Mercer, PA | Dennis, MA | United States |
| Population | 1,808 | 14,664 | 329,725,481 |
| Female Population | 56.9% | 50.4% | 50.5% |
| Male Population | 43.1% | 49.6% | 49.5% |
| Median Age | 42.7 | 57.5 | 38.4 |
| space3 | | | |
| Population - 2010 | 2,042 | 14,220 | 309,327,143 |
| Population - 2000 | 2,391 | 15,973 | 285,036,114 |
| Population - 1990 | 2,444 | 13,864 | 251,960,433 |
| Pop. 2000 to Now | -22.0% | -13.0% | 15.6% |
| Pop. 1990 to Now | -23.7% | 0.2% | 30.8% |
| space4 | | | |
| Population Density | 1,587.4 | 715.0 | 93.4 |
| Land Area | 1.1 | 20.5 | 3,531,905.4 |
| Water Area | 0.0 | 1.8 | 264,836.8 |
| space | | | |
| Est. Total Population By Age | | | |
| | Mercer, PA | Dennis, MA | United States |
| Age 0 to 4 | 8.8% | 3.3% | 5.9% |
| Age 5 to 9 | 4.8% | 2.8% | 6.1% |
| Age 10 to 14 | 3.9% | 2.9% | 6.6% |
| Age 15 to 17 | 2.5% | 2.1% | 3.9% |
| Age 18 to 20 | 3.5% | 2.0% | 4.0% |
| Age 21 to 24 | 4.1% | 4.8% | 5.2% |
| Age 25 to 34 | 10.9% | 8.1% | 13.8% |
| Age 35 to 44 | 14.0% | 8.4% | 12.9% |
| Age 45 to 54 | 13.9% | 11.9% | 12.6% |
| Age 55 to 59 | 4.3% | 9.6% | 6.7% |
| Age 60 to 64 | 9.6% | 9.1% | 6.3% |
| Age 65 to 74 | 9.7% | 19.9% | 9.6% |
| Age 75 to 84 | 6.2% | 11.0% | 4.5% |
| Age 85 and over | 3.7% | 4.1% | 1.9% |
| space1 | | | |
| Race | | | |
| | Mercer, PA | Dennis, MA | United States |
| White | 98.1% | 89.4% | 59.4% |
| Black | 0.0% | 2.8% | 12.2% |
| Asian | 0.7% | 0.7% | 5.6% |
| Native American | 0.8% | 0.5% | 0.6% |
| Hawaiian, Pacific Islander | 0.0% | 0.1% | 0.2% |
| Other | 0.0% | 0.3% | 0.4% |
| Two or More Races | 0.4% | 1.8% | 3.2% |
| Hispanic | 0.0% | 4.3% | 18.4% |
| space2 | | | |
| Marriage & Family | | | |
| | Mercer, PA | Dennis, MA | United States |
| Married Population | 48.3% | 51.3% | 49.8% |
| Currently Married | 47.7% | 50.7% | 48.0% |
| Married but Separated | 0.6% | 0.6% | 1.8% |
| Single Population | 51.7% | 48.7% | 50.2% |
| Never Married | 28.6% | 25.9% | 33.8% |
| Divorced | 13.1% | 14.3% | 10.8% |
| Widowed | 10.0% | 8.6% | 5.6% |
| space5 | | | |
| Household Size | 2.17 | 2.08 | 2.60 |
| Households | 834 | 6,989 | 124,010,992 |
| Family Households | 486 | 3,999 | 80,755,759 |
| Married couple, w/children | 29.2% | 12.4% | 30.5% |
| Married couple, no children | 36.8% | 61.0% | 42.9% |
| Non Family Households | 348 | 2,990 | 43,255,233 |
| Single householder, w/children | 17.3% | 13.1% | 15.8% |
| Single householder, no children | 16.7% | 13.6% | 10.8% |