| | Frederick, MD | Mount Pleasant, SC | United States |
| Population | 76,376 | 88,900 | 329,725,481 |
| Female Population | 51.0% | 51.0% | 50.5% |
| Male Population | 49.0% | 49.0% | 49.5% |
| Median Age | 36.9 | 41.8 | 38.4 |
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| Population - 2010 | 65,508 | 68,553 | 309,327,143 |
| Population - 2000 | 52,767 | 47,609 | 285,036,114 |
| Population - 1990 | 40,148 | 30,108 | 251,960,433 |
| Pop. 2000 to Now | 38.9% | 94.9% | 15.6% |
| Pop. 1990 to Now | 82.6% | 208.2% | 30.8% |
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| Population Density | 3,297.3 | 1,969.1 | 93.4 |
| Land Area | 23.2 | 45.1 | 3,531,905.4 |
| Water Area | 0.2 | 7.5 | 264,836.8 |
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| Est. Total Population By Age | | | |
| | Frederick, MD | Mount Pleasant, SC | United States |
| Age 0 to 4 | 5.9% | 5.7% | 5.9% |
| Age 5 to 9 | 5.8% | 5.3% | 6.1% |
| Age 10 to 14 | 6.7% | 7.6% | 6.6% |
| Age 15 to 17 | 3.7% | 4.2% | 3.9% |
| Age 18 to 20 | 3.6% | 1.6% | 4.0% |
| Age 21 to 24 | 5.5% | 2.8% | 5.2% |
| Age 25 to 34 | 15.7% | 12.7% | 13.8% |
| Age 35 to 44 | 14.3% | 15.5% | 12.9% |
| Age 45 to 54 | 13.1% | 13.7% | 12.6% |
| Age 55 to 59 | 6.9% | 6.7% | 6.7% |
| Age 60 to 64 | 5.0% | 6.8% | 6.3% |
| Age 65 to 74 | 8.0% | 11.1% | 9.6% |
| Age 75 to 84 | 3.9% | 4.2% | 4.5% |
| Age 85 and over | 1.8% | 2.2% | 1.9% |
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| Race | | | |
| | Frederick, MD | Mount Pleasant, SC | United States |
| White | 54.9% | 89.9% | 59.4% |
| Black | 17.1% | 3.3% | 12.2% |
| Asian | 5.1% | 2.0% | 5.6% |
| Native American | 0.2% | 0.1% | 0.6% |
| Hawaiian, Pacific Islander | 0.0% | 0.0% | 0.2% |
| Other | 0.2% | 0.1% | 0.4% |
| Two or More Races | 4.9% | 2.3% | 3.2% |
| Hispanic | 17.5% | 2.3% | 18.4% |
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| Marriage & Family | | | |
| | Frederick, MD | Mount Pleasant, SC | United States |
| Married Population | 47.9% | 61.6% | 49.8% |
| Currently Married | 45.7% | 61.0% | 48.0% |
| Married but Separated | 2.2% | 0.6% | 1.8% |
| Single Population | 52.1% | 38.4% | 50.2% |
| Never Married | 35.0% | 24.4% | 33.8% |
| Divorced | 11.7% | 8.7% | 10.8% |
| Widowed | 5.4% | 5.2% | 5.6% |
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| Household Size | 2.43 | 2.41 | 2.60 |
| Households | 30,644 | 36,673 | 124,010,992 |
| Family Households | 18,686 | 24,488 | 80,755,759 |
| Married couple, w/children | 34.7% | 38.0% | 30.5% |
| Married couple, no children | 35.7% | 48.7% | 42.9% |
| Non Family Households | 11,958 | 12,185 | 43,255,233 |
| Single householder, w/children | 18.2% | 8.4% | 15.8% |
| Single householder, no children | 11.4% | 4.9% | 10.8% |