| | Olney, MD | Columbia, SC | United States |
| Population | 35,815 | 137,276 | 329,725,481 |
| Female Population | 50.6% | 50.0% | 50.5% |
| Male Population | 49.4% | 50.0% | 49.5% |
| Median Age | 42.4 | 28.2 | 38.4 |
| space3 | | | |
| Population - 2010 | 33,167 | 130,909 | 309,327,143 |
| Population - 2000 | 31,438 | 116,278 | 285,036,114 |
| Population - 1990 | 23,019 | 98,052 | 251,960,433 |
| Pop. 2000 to Now | 15.8% | 13.6% | 15.6% |
| Pop. 1990 to Now | 58.2% | 34.8% | 30.8% |
| space4 | | | |
| Population Density | 2,210.8 | 1,009.4 | 93.4 |
| Land Area | 16.2 | 136.0 | 3,531,905.4 |
| Water Area | 0.0 | 2.8 | 264,836.8 |
| space | | | |
| Est. Total Population By Age | | | |
| | Olney, MD | Columbia, SC | United States |
| Age 0 to 4 | 5.6% | 5.3% | 5.9% |
| Age 5 to 9 | 6.0% | 4.1% | 6.1% |
| Age 10 to 14 | 7.1% | 4.8% | 6.6% |
| Age 15 to 17 | 5.2% | 3.2% | 3.9% |
| Age 18 to 20 | 3.6% | 14.6% | 4.0% |
| Age 21 to 24 | 4.7% | 11.9% | 5.2% |
| Age 25 to 34 | 8.8% | 17.0% | 13.8% |
| Age 35 to 44 | 12.5% | 10.3% | 12.9% |
| Age 45 to 54 | 15.7% | 10.0% | 12.6% |
| Age 55 to 59 | 7.6% | 4.3% | 6.7% |
| Age 60 to 64 | 6.9% | 4.1% | 6.3% |
| Age 65 to 74 | 9.5% | 6.4% | 9.6% |
| Age 75 to 84 | 4.5% | 2.9% | 4.5% |
| Age 85 and over | 2.2% | 1.0% | 1.9% |
| space1 | | | |
| Race | | | |
| | Olney, MD | Columbia, SC | United States |
| White | 57.9% | 48.0% | 59.4% |
| Black | 13.6% | 40.3% | 12.2% |
| Asian | 12.7% | 2.6% | 5.6% |
| Native American | 0.2% | 0.2% | 0.6% |
| Hawaiian, Pacific Islander | 0.0% | 0.2% | 0.2% |
| Other | 0.4% | 0.3% | 0.4% |
| Two or More Races | 5.4% | 2.8% | 3.2% |
| Hispanic | 9.8% | 5.6% | 18.4% |
| space2 | | | |
| Marriage & Family | | | |
| | Olney, MD | Columbia, SC | United States |
| Married Population | 61.0% | 31.9% | 49.8% |
| Currently Married | 59.6% | 29.6% | 48.0% |
| Married but Separated | 1.3% | 2.3% | 1.8% |
| Single Population | 39.0% | 68.1% | 50.2% |
| Never Married | 28.2% | 55.7% | 33.8% |
| Divorced | 7.2% | 8.4% | 10.8% |
| Widowed | 3.7% | 4.0% | 5.6% |
| space5 | | | |
| Household Size | 3.00 | 2.19 | 2.60 |
| Households | 11,899 | 50,372 | 124,010,992 |
| Family Households | 9,840 | 24,276 | 80,755,759 |
| Married couple, w/children | 38.5% | 25.6% | 30.5% |
| Married couple, no children | 45.4% | 37.4% | 42.9% |
| Non Family Households | 2,059 | 26,096 | 43,255,233 |
| Single householder, w/children | 9.2% | 25.2% | 15.8% |
| Single householder, no children | 6.9% | 11.8% | 10.8% |