| | Portsmouth, OH | Marietta, OH | United States |
| Population | 18,369 | 13,559 | 329,725,481 |
| Female Population | 53.3% | 50.8% | 50.5% |
| Male Population | 46.7% | 49.2% | 49.5% |
| Median Age | 36.5 | 38.5 | 38.4 |
| space3 | | | |
| Population - 2010 | 20,168 | 14,082 | 309,327,143 |
| Population - 2000 | 20,909 | 14,515 | 285,036,114 |
| Population - 1990 | 22,676 | 15,026 | 251,960,433 |
| Pop. 2000 to Now | -5.6% | -7.9% | 15.6% |
| Pop. 1990 to Now | -12.9% | -11.1% | 30.8% |
| space4 | | | |
| Population Density | 1,711.3 | 1,608.6 | 93.4 |
| Land Area | 10.7 | 8.4 | 3,531,905.4 |
| Water Area | 0.3 | 0.3 | 264,836.8 |
| space | | | |
| Est. Total Population By Age | | | |
| | Portsmouth, OH | Marietta, OH | United States |
| Age 0 to 4 | 5.8% | 6.2% | 5.9% |
| Age 5 to 9 | 6.6% | 4.1% | 6.1% |
| Age 10 to 14 | 6.0% | 6.2% | 6.6% |
| Age 15 to 17 | 3.9% | 2.7% | 3.9% |
| Age 18 to 20 | 5.0% | 5.6% | 4.0% |
| Age 21 to 24 | 6.8% | 7.8% | 5.2% |
| Age 25 to 34 | 14.0% | 13.7% | 13.8% |
| Age 35 to 44 | 11.6% | 10.0% | 12.9% |
| Age 45 to 54 | 9.5% | 9.6% | 12.6% |
| Age 55 to 59 | 6.7% | 5.8% | 6.7% |
| Age 60 to 64 | 6.1% | 7.2% | 6.3% |
| Age 65 to 74 | 10.2% | 10.6% | 9.6% |
| Age 75 to 84 | 6.0% | 6.9% | 4.5% |
| Age 85 and over | 1.7% | 3.6% | 1.9% |
| space1 | | | |
| Race | | | |
| | Portsmouth, OH | Marietta, OH | United States |
| White | 85.3% | 92.4% | 59.4% |
| Black | 6.4% | 2.4% | 12.2% |
| Asian | 1.2% | 1.2% | 5.6% |
| Native American | 0.1% | 0.3% | 0.6% |
| Hawaiian, Pacific Islander | 0.0% | 0.0% | 0.2% |
| Other | 0.0% | 0.3% | 0.4% |
| Two or More Races | 4.2% | 1.7% | 3.2% |
| Hispanic | 2.8% | 1.7% | 18.4% |
| space2 | | | |
| Marriage & Family | | | |
| | Portsmouth, OH | Marietta, OH | United States |
| Married Population | 35.8% | 39.2% | 49.8% |
| Currently Married | 32.5% | 37.4% | 48.0% |
| Married but Separated | 3.4% | 1.8% | 1.8% |
| Single Population | 64.2% | 60.8% | 50.2% |
| Never Married | 41.0% | 35.8% | 33.8% |
| Divorced | 14.4% | 15.7% | 10.8% |
| Widowed | 8.8% | 9.3% | 5.6% |
| space5 | | | |
| Household Size | 2.35 | 2.14 | 2.60 |
| Households | 7,259 | 5,775 | 124,010,992 |
| Family Households | 3,950 | 3,143 | 80,755,759 |
| Married couple, w/children | 22.2% | 17.8% | 30.5% |
| Married couple, no children | 33.4% | 43.1% | 42.9% |
| Non Family Households | 3,309 | 2,632 | 43,255,233 |
| Single householder, w/children | 28.5% | 27.8% | 15.8% |
| Single householder, no children | 15.8% | 11.3% | 10.8% |