| | Secretary, MD | Dover, PA | United States |
| Population | 648 | 2,159 | 329,725,481 |
| Female Population | 45.4% | 48.3% | 50.5% |
| Male Population | 54.6% | 51.7% | 49.5% |
| Median Age | 33.4 | 36.8 | 38.4 |
| space3 | | | |
| Population - 2010 | 529 | 2,006 | 309,327,143 |
| Population - 2000 | 503 | 1,815 | 285,036,114 |
| Population - 1990 | 528 | 1,884 | 251,960,433 |
| Pop. 2000 to Now | -1.4% | 9.2% | 15.6% |
| Pop. 1990 to Now | -6.1% | 5.2% | 30.8% |
| space4 | | | |
| Population Density | 2,226.8 | 3,976.1 | 93.4 |
| Land Area | 0.3 | 0.5 | 3,531,905.4 |
| Water Area | 0.0 | 0.0 | 264,836.8 |
| space | | | |
| Est. Total Population By Age | | | |
| | Secretary, MD | Dover, PA | United States |
| Age 0 to 4 | 3.1% | 4.3% | 5.9% |
| Age 5 to 9 | 5.2% | 7.1% | 6.1% |
| Age 10 to 14 | 19.3% | 12.9% | 6.6% |
| Age 15 to 17 | 5.4% | 2.7% | 3.9% |
| Age 18 to 20 | 4.6% | 2.7% | 4.0% |
| Age 21 to 24 | 2.6% | 5.0% | 5.2% |
| Age 25 to 34 | 10.5% | 12.4% | 13.8% |
| Age 35 to 44 | 19.1% | 10.0% | 12.9% |
| Age 45 to 54 | 7.9% | 18.5% | 12.6% |
| Age 55 to 59 | 5.2% | 3.6% | 6.7% |
| Age 60 to 64 | 4.5% | 5.7% | 6.3% |
| Age 65 to 74 | 6.9% | 10.8% | 9.6% |
| Age 75 to 84 | 4.5% | 3.3% | 4.5% |
| Age 85 and over | 1.1% | 1.0% | 1.9% |
| space1 | | | |
| Race | | | |
| | Secretary, MD | Dover, PA | United States |
| White | 65.0% | 89.3% | 59.4% |
| Black | 0.2% | 3.1% | 12.2% |
| Asian | 0.0% | 4.7% | 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 | 2.8% | 1.3% | 3.2% |
| Hispanic | 32.1% | 1.7% | 18.4% |
| space2 | | | |
| Marriage & Family | | | |
| | Secretary, MD | Dover, PA | United States |
| Married Population | 40.9% | 50.9% | 49.8% |
| Currently Married | 37.5% | 49.0% | 48.0% |
| Married but Separated | 3.4% | 1.9% | 1.8% |
| Single Population | 59.1% | 49.1% | 50.2% |
| Never Married | 39.4% | 32.9% | 33.8% |
| Divorced | 12.4% | 8.3% | 10.8% |
| Widowed | 7.2% | 7.9% | 5.6% |
| space5 | | | |
| Household Size | 2.93 | 2.64 | 2.60 |
| Households | 221 | 817 | 124,010,992 |
| Family Households | 124 | 578 | 80,755,759 |
| Married couple, w/children | 46.0% | 33.7% | 30.5% |
| Married couple, no children | 28.2% | 32.9% | 42.9% |
| Non Family Households | 97 | 239 | 43,255,233 |
| Single householder, w/children | 13.7% | 20.4% | 15.8% |
| Single householder, no children | 12.1% | 13.0% | 10.8% |