| | Mount Pleasant, SC | Happy Valley, OR | United States |
| Population | 88,900 | 23,442 | 329,725,481 |
| Female Population | 51.0% | 51.1% | 50.5% |
| Male Population | 49.0% | 49.0% | 49.5% |
| Median Age | 41.8 | 39 | 38.4 |
| space3 | | | |
| Population - 2010 | 68,553 | 15,337 | 309,327,143 |
| Population - 2000 | 47,609 | 4,519 | 285,036,114 |
| Population - 1990 | 30,108 | 1,519 | 251,960,433 |
| Pop. 2000 to Now | 94.9% | 426.2% | 15.6% |
| Pop. 1990 to Now | 208.2% | 1,465.6% | 30.8% |
| space4 | | | |
| Population Density | 1,969.1 | 2,641.1 | 93.4 |
| Land Area | 45.1 | 8.9 | 3,531,905.4 |
| Water Area | 7.5 | 0.0 | 264,836.8 |
| space | | | |
| Est. Total Population By Age | | | |
| | Mount Pleasant, SC | Happy Valley, OR | United States |
| Age 0 to 4 | 5.7% | 4.2% | 5.9% |
| Age 5 to 9 | 5.3% | 9.2% | 6.1% |
| Age 10 to 14 | 7.6% | 9.2% | 6.6% |
| Age 15 to 17 | 4.2% | 5.4% | 3.9% |
| Age 18 to 20 | 1.6% | 3.9% | 4.0% |
| Age 21 to 24 | 2.8% | 3.7% | 5.2% |
| Age 25 to 34 | 12.7% | 9.6% | 13.8% |
| Age 35 to 44 | 15.5% | 15.9% | 12.9% |
| Age 45 to 54 | 13.7% | 14.3% | 12.6% |
| Age 55 to 59 | 6.7% | 5.2% | 6.7% |
| Age 60 to 64 | 6.8% | 6.0% | 6.3% |
| Age 65 to 74 | 11.1% | 7.7% | 9.6% |
| Age 75 to 84 | 4.2% | 3.5% | 4.5% |
| Age 85 and over | 2.2% | 2.3% | 1.9% |
| space1 | | | |
| Race | | | |
| | Mount Pleasant, SC | Happy Valley, OR | United States |
| White | 89.9% | 63.6% | 59.4% |
| Black | 3.3% | 0.9% | 12.2% |
| Asian | 2.0% | 19.8% | 5.6% |
| Native American | 0.1% | 0.4% | 0.6% |
| Hawaiian, Pacific Islander | 0.0% | 0.1% | 0.2% |
| Other | 0.1% | 1.6% | 0.4% |
| Two or More Races | 2.3% | 7.2% | 3.2% |
| Hispanic | 2.3% | 6.4% | 18.4% |
| space2 | | | |
| Marriage & Family | | | |
| | Mount Pleasant, SC | Happy Valley, OR | United States |
| Married Population | 61.6% | 58.3% | 49.8% |
| Currently Married | 61.0% | 58.0% | 48.0% |
| Married but Separated | 0.6% | 0.4% | 1.8% |
| Single Population | 38.4% | 41.7% | 50.2% |
| Never Married | 24.4% | 28.8% | 33.8% |
| Divorced | 8.7% | 8.7% | 10.8% |
| Widowed | 5.2% | 4.2% | 5.6% |
| space5 | | | |
| Household Size | 2.41 | 3.15 | 2.60 |
| Households | 36,673 | 7,432 | 124,010,992 |
| Family Households | 24,488 | 5,978 | 80,755,759 |
| Married couple, w/children | 38.0% | 40.7% | 30.5% |
| Married couple, no children | 48.7% | 42.0% | 42.9% |
| Non Family Households | 12,185 | 1,454 | 43,255,233 |
| Single householder, w/children | 8.4% | 12.7% | 15.8% |
| Single householder, no children | 4.9% | 4.5% | 10.8% |