| | Petersburg, VA | Irmo, SC | United States |
| Population | 33,229 | 11,581 | 329,725,481 |
| Female Population | 53.8% | 54.2% | 50.5% |
| Male Population | 46.3% | 45.8% | 49.5% |
| Median Age | 37.2 | 39.6 | 38.4 |
| space3 | | | |
| Population - 2010 | 32,502 | 11,167 | 309,327,143 |
| Population - 2000 | 33,740 | 11,039 | 285,036,114 |
| Population - 1990 | 38,386 | 11,280 | 251,960,433 |
| Pop. 2000 to Now | -9.8% | 15.4% | 15.6% |
| Pop. 1990 to Now | -20.7% | 12.9% | 30.8% |
| space4 | | | |
| Population Density | 1,462.5 | 1,714.4 | 93.4 |
| Land Area | 22.7 | 6.8 | 3,531,905.4 |
| Water Area | 0.2 | 0.0 | 264,836.8 |
| space | | | |
| Est. Total Population By Age | | | |
| | Petersburg, VA | Irmo, SC | United States |
| Age 0 to 4 | 7.3% | 4.1% | 5.9% |
| Age 5 to 9 | 7.1% | 6.7% | 6.1% |
| Age 10 to 14 | 4.2% | 4.9% | 6.6% |
| Age 15 to 17 | 3.2% | 4.6% | 3.9% |
| Age 18 to 20 | 3.6% | 2.2% | 4.0% |
| Age 21 to 24 | 5.2% | 4.0% | 5.2% |
| Age 25 to 34 | 16.2% | 17.6% | 13.8% |
| Age 35 to 44 | 10.8% | 11.1% | 12.9% |
| Age 45 to 54 | 11.8% | 12.7% | 12.6% |
| Age 55 to 59 | 6.8% | 11.8% | 6.7% |
| Age 60 to 64 | 6.9% | 5.0% | 6.3% |
| Age 65 to 74 | 10.0% | 8.8% | 9.6% |
| Age 75 to 84 | 4.4% | 5.0% | 4.5% |
| Age 85 and over | 2.3% | 1.4% | 1.9% |
| space1 | | | |
| Race | | | |
| | Petersburg, VA | Irmo, SC | United States |
| White | 15.0% | 65.4% | 59.4% |
| Black | 75.8% | 25.6% | 12.2% |
| Asian | 1.0% | 3.9% | 5.6% |
| Native American | 0.0% | 0.0% | 0.6% |
| Hawaiian, Pacific Islander | 0.1% | 0.0% | 0.2% |
| Other | 0.1% | 0.0% | 0.4% |
| Two or More Races | 2.8% | 2.7% | 3.2% |
| Hispanic | 5.1% | 2.5% | 18.4% |
| space2 | | | |
| Marriage & Family | | | |
| | Petersburg, VA | Irmo, SC | United States |
| Married Population | 28.3% | 57.7% | 49.8% |
| Currently Married | 24.4% | 56.8% | 48.0% |
| Married but Separated | 3.9% | 0.9% | 1.8% |
| Single Population | 71.7% | 42.3% | 50.2% |
| Never Married | 50.4% | 28.4% | 33.8% |
| Divorced | 13.9% | 9.6% | 10.8% |
| Widowed | 7.4% | 4.4% | 5.6% |
| space5 | | | |
| Household Size | 2.26 | 2.53 | 2.60 |
| Households | 14,464 | 4,567 | 124,010,992 |
| Family Households | 6,592 | 3,350 | 80,755,759 |
| Married couple, w/children | 13.5% | 26.1% | 30.5% |
| Married couple, no children | 26.8% | 54.2% | 42.9% |
| Non Family Households | 7,872 | 1,217 | 43,255,233 |
| Single householder, w/children | 31.5% | 15.7% | 15.8% |
| Single householder, no children | 28.3% | 4.0% | 10.8% |