| | Portsmouth, RI | Millville, DE | United States |
| Population | 17,802 | 1,790 | 329,725,481 |
| Female Population | 49.4% | 57.5% | 50.5% |
| Male Population | 50.6% | 42.5% | 49.5% |
| Median Age | 48.4 | 64.1 | 38.4 |
| space3 | | | |
| Population - 2010 | 17,393 | 534 | 309,327,143 |
| Population - 2000 | 17,149 | 259 | 285,036,114 |
| Population - 1990 | 16,857 | 206 | 251,960,433 |
| Pop. 2000 to Now | -0.2% | 151.7% | 15.6% |
| Pop. 1990 to Now | 1.5% | 216.5% | 30.8% |
| space4 | | | |
| Population Density | 774.2 | 701.1 | 93.4 |
| Land Area | 23.0 | 2.6 | 3,531,905.4 |
| Water Area | 36.3 | 0.0 | 264,836.8 |
| space | | | |
| Est. Total Population By Age | | | |
| | Portsmouth, RI | Millville, DE | United States |
| Age 0 to 4 | 4.1% | 3.2% | 5.9% |
| Age 5 to 9 | 5.0% | 1.5% | 6.1% |
| Age 10 to 14 | 6.7% | 1.7% | 6.6% |
| Age 15 to 17 | 5.0% | 0.7% | 3.9% |
| Age 18 to 20 | 2.9% | 0.7% | 4.0% |
| Age 21 to 24 | 3.5% | 0.7% | 5.2% |
| Age 25 to 34 | 7.6% | 9.0% | 13.8% |
| Age 35 to 44 | 10.7% | 2.7% | 12.9% |
| Age 45 to 54 | 15.7% | 7.0% | 12.6% |
| Age 55 to 59 | 7.8% | 7.2% | 6.7% |
| Age 60 to 64 | 7.9% | 18.3% | 6.3% |
| Age 65 to 74 | 13.7% | 38.4% | 9.6% |
| Age 75 to 84 | 6.9% | 6.3% | 4.5% |
| Age 85 and over | 2.6% | 2.5% | 1.9% |
| space1 | | | |
| Race | | | |
| | Portsmouth, RI | Millville, DE | United States |
| White | 90.6% | 94.1% | 59.4% |
| Black | 1.3% | 0.3% | 12.2% |
| Asian | 0.7% | 0.3% | 5.6% |
| Native American | 0.0% | 0.0% | 0.6% |
| Hawaiian, Pacific Islander | 0.0% | 0.0% | 0.2% |
| Other | 0.1% | 0.0% | 0.4% |
| Two or More Races | 2.1% | 1.3% | 3.2% |
| Hispanic | 5.3% | 3.9% | 18.4% |
| space2 | | | |
| Marriage & Family | | | |
| | Portsmouth, RI | Millville, DE | United States |
| Married Population | 59.2% | 72.9% | 49.8% |
| Currently Married | 59.0% | 71.5% | 48.0% |
| Married but Separated | 0.2% | 1.4% | 1.8% |
| Single Population | 40.8% | 27.1% | 50.2% |
| Never Married | 23.5% | 9.6% | 33.8% |
| Divorced | 11.0% | 11.8% | 10.8% |
| Widowed | 6.3% | 5.6% | 5.6% |
| space5 | | | |
| Household Size | 2.40 | 1.88 | 2.60 |
| Households | 7,278 | 953 | 124,010,992 |
| Family Households | 4,902 | 651 | 80,755,759 |
| Married couple, w/children | 34.7% | 10.8% | 30.5% |
| Married couple, no children | 51.9% | 82.0% | 42.9% |
| Non Family Households | 2,376 | 302 | 43,255,233 |
| Single householder, w/children | 6.4% | 2.5% | 15.8% |
| Single householder, no children | 7.0% | 4.8% | 10.8% |