| | Sumter, SC | Williamsport, PA | United States |
| Population | 42,920 | 27,908 | 329,725,481 |
| Female Population | 51.2% | 49.5% | 50.5% |
| Male Population | 48.8% | 50.5% | 49.5% |
| Median Age | 32.3 | 31 | 38.4 |
| space3 | | | |
| Population - 2010 | 40,564 | 29,392 | 309,327,143 |
| Population - 2000 | 39,643 | 30,706 | 285,036,114 |
| Population - 1990 | 41,943 | 31,933 | 251,960,433 |
| Pop. 2000 to Now | -0.5% | -8.3% | 15.6% |
| Pop. 1990 to Now | -6.0% | -11.8% | 30.8% |
| space4 | | | |
| Population Density | 1,317.3 | 3,196.4 | 93.4 |
| Land Area | 32.6 | 8.7 | 3,531,905.4 |
| Water Area | 0.2 | 0.7 | 264,836.8 |
| space | | | |
| Est. Total Population By Age | | | |
| | Sumter, SC | Williamsport, PA | United States |
| Age 0 to 4 | 8.0% | 5.5% | 5.9% |
| Age 5 to 9 | 7.4% | 6.2% | 6.1% |
| Age 10 to 14 | 7.6% | 5.0% | 6.6% |
| Age 15 to 17 | 4.0% | 3.6% | 3.9% |
| Age 18 to 20 | 4.4% | 11.6% | 4.0% |
| Age 21 to 24 | 6.6% | 7.8% | 5.2% |
| Age 25 to 34 | 14.8% | 15.6% | 13.8% |
| Age 35 to 44 | 10.2% | 10.0% | 12.9% |
| Age 45 to 54 | 10.1% | 10.5% | 12.6% |
| Age 55 to 59 | 5.7% | 6.4% | 6.7% |
| Age 60 to 64 | 5.3% | 4.7% | 6.3% |
| Age 65 to 74 | 8.6% | 8.1% | 9.6% |
| Age 75 to 84 | 4.0% | 3.6% | 4.5% |
| Age 85 and over | 3.1% | 1.4% | 1.9% |
| space1 | | | |
| Race | | | |
| | Sumter, SC | Williamsport, PA | United States |
| White | 38.9% | 77.0% | 59.4% |
| Black | 48.0% | 14.3% | 12.2% |
| Asian | 2.1% | 1.4% | 5.6% |
| Native American | 0.2% | 0.3% | 0.6% |
| Hawaiian, Pacific Islander | 0.0% | 0.0% | 0.2% |
| Other | 0.6% | 0.1% | 0.4% |
| Two or More Races | 2.9% | 4.4% | 3.2% |
| Hispanic | 7.2% | 2.4% | 18.4% |
| space2 | | | |
| Marriage & Family | | | |
| | Sumter, SC | Williamsport, PA | United States |
| Married Population | 47.5% | 32.9% | 49.8% |
| Currently Married | 43.4% | 29.7% | 48.0% |
| Married but Separated | 4.1% | 3.2% | 1.8% |
| Single Population | 52.5% | 67.1% | 50.2% |
| Never Married | 35.0% | 51.2% | 33.8% |
| Divorced | 10.0% | 11.0% | 10.8% |
| Widowed | 7.5% | 4.9% | 5.6% |
| space5 | | | |
| Household Size | 2.50 | 2.22 | 2.60 |
| Households | 16,595 | 11,017 | 124,010,992 |
| Family Households | 10,400 | 5,822 | 80,755,759 |
| Married couple, w/children | 24.6% | 19.2% | 30.5% |
| Married couple, no children | 38.4% | 37.2% | 42.9% |
| Non Family Households | 6,195 | 5,195 | 43,255,233 |
| Single householder, w/children | 23.7% | 30.6% | 15.8% |
| Single householder, no children | 13.3% | 13.0% | 10.8% |