| | Irmo, SC | Mount Pleasant, SC | United States |
| Population | 11,581 | 88,900 | 329,725,481 |
| Female Population | 54.2% | 51.0% | 50.5% |
| Male Population | 45.8% | 49.0% | 49.5% |
| Median Age | 39.6 | 41.8 | 38.4 |
| space3 | | | |
| Population - 2010 | 11,167 | 68,553 | 309,327,143 |
| Population - 2000 | 11,039 | 47,609 | 285,036,114 |
| Population - 1990 | 11,280 | 30,108 | 251,960,433 |
| Pop. 2000 to Now | 15.4% | 94.9% | 15.6% |
| Pop. 1990 to Now | 12.9% | 208.2% | 30.8% |
| space4 | | | |
| Population Density | 1,714.4 | 1,969.1 | 93.4 |
| Land Area | 6.8 | 45.1 | 3,531,905.4 |
| Water Area | 0.0 | 7.5 | 264,836.8 |
| space | | | |
| Est. Total Population By Age | | | |
| | Irmo, SC | Mount Pleasant, SC | United States |
| Age 0 to 4 | 4.1% | 5.7% | 5.9% |
| Age 5 to 9 | 6.7% | 5.3% | 6.1% |
| Age 10 to 14 | 4.9% | 7.6% | 6.6% |
| Age 15 to 17 | 4.6% | 4.2% | 3.9% |
| Age 18 to 20 | 2.2% | 1.6% | 4.0% |
| Age 21 to 24 | 4.0% | 2.8% | 5.2% |
| Age 25 to 34 | 17.6% | 12.7% | 13.8% |
| Age 35 to 44 | 11.1% | 15.5% | 12.9% |
| Age 45 to 54 | 12.7% | 13.7% | 12.6% |
| Age 55 to 59 | 11.8% | 6.7% | 6.7% |
| Age 60 to 64 | 5.0% | 6.8% | 6.3% |
| Age 65 to 74 | 8.8% | 11.1% | 9.6% |
| Age 75 to 84 | 5.0% | 4.2% | 4.5% |
| Age 85 and over | 1.4% | 2.2% | 1.9% |
| space1 | | | |
| Race | | | |
| | Irmo, SC | Mount Pleasant, SC | United States |
| White | 65.4% | 89.9% | 59.4% |
| Black | 25.6% | 3.3% | 12.2% |
| Asian | 3.9% | 2.0% | 5.6% |
| Native American | 0.0% | 0.1% | 0.6% |
| Hawaiian, Pacific Islander | 0.0% | 0.0% | 0.2% |
| Other | 0.0% | 0.1% | 0.4% |
| Two or More Races | 2.7% | 2.3% | 3.2% |
| Hispanic | 2.5% | 2.3% | 18.4% |
| space2 | | | |
| Marriage & Family | | | |
| | Irmo, SC | Mount Pleasant, SC | United States |
| Married Population | 57.7% | 61.6% | 49.8% |
| Currently Married | 56.8% | 61.0% | 48.0% |
| Married but Separated | 0.9% | 0.6% | 1.8% |
| Single Population | 42.3% | 38.4% | 50.2% |
| Never Married | 28.4% | 24.4% | 33.8% |
| Divorced | 9.6% | 8.7% | 10.8% |
| Widowed | 4.4% | 5.2% | 5.6% |
| space5 | | | |
| Household Size | 2.53 | 2.41 | 2.60 |
| Households | 4,567 | 36,673 | 124,010,992 |
| Family Households | 3,350 | 24,488 | 80,755,759 |
| Married couple, w/children | 26.1% | 38.0% | 30.5% |
| Married couple, no children | 54.2% | 48.7% | 42.9% |
| Non Family Households | 1,217 | 12,185 | 43,255,233 |
| Single householder, w/children | 15.7% | 8.4% | 15.8% |
| Single householder, no children | 4.0% | 4.9% | 10.8% |