| | St. Petersburg, FL | Quincy, MA | United States |
| Population | 258,245 | 100,544 | 329,725,481 |
| Female Population | 51.5% | 49.8% | 50.5% |
| Male Population | 48.5% | 50.2% | 49.5% |
| Median Age | 42.9 | 38.3 | 38.4 |
| space3 | | | |
| Population - 2010 | 245,220 | 92,457 | 309,327,143 |
| Population - 2000 | 248,232 | 88,025 | 285,036,114 |
| Population - 1990 | 238,629 | 84,985 | 251,960,433 |
| Pop. 2000 to Now | 7.9% | 7.3% | 15.6% |
| Pop. 1990 to Now | 12.2% | 11.1% | 30.8% |
| space4 | | | |
| Population Density | 4,175.5 | 6,067.8 | 93.4 |
| Land Area | 61.8 | 16.6 | 3,531,905.4 |
| Water Area | 76.2 | 10.3 | 264,836.8 |
| space | | | |
| Est. Total Population By Age | | | |
| | St. Petersburg, FL | Quincy, MA | United States |
| Age 0 to 4 | 4.9% | 5.2% | 5.9% |
| Age 5 to 9 | 4.9% | 3.8% | 6.1% |
| Age 10 to 14 | 4.6% | 3.8% | 6.6% |
| Age 15 to 17 | 2.7% | 2.0% | 3.9% |
| Age 18 to 20 | 2.9% | 2.0% | 4.0% |
| Age 21 to 24 | 4.7% | 5.4% | 5.2% |
| Age 25 to 34 | 15.6% | 21.6% | 13.8% |
| Age 35 to 44 | 12.4% | 15.1% | 12.9% |
| Age 45 to 54 | 12.9% | 11.2% | 12.6% |
| Age 55 to 59 | 7.9% | 6.8% | 6.7% |
| Age 60 to 64 | 7.4% | 6.3% | 6.3% |
| Age 65 to 74 | 11.3% | 9.9% | 9.6% |
| Age 75 to 84 | 5.7% | 4.1% | 4.5% |
| Age 85 and over | 2.3% | 2.8% | 1.9% |
| space1 | | | |
| Race | | | |
| | St. Petersburg, FL | Quincy, MA | United States |
| White | 63.9% | 56.7% | 59.4% |
| Black | 20.7% | 5.8% | 12.2% |
| Asian | 3.3% | 29.8% | 5.6% |
| Native American | 0.1% | 0.1% | 0.6% |
| Hawaiian, Pacific Islander | 0.0% | 0.1% | 0.2% |
| Other | 0.4% | 0.5% | 0.4% |
| Two or More Races | 3.3% | 2.4% | 3.2% |
| Hispanic | 8.2% | 4.6% | 18.4% |
| space2 | | | |
| Marriage & Family | | | |
| | St. Petersburg, FL | Quincy, MA | United States |
| Married Population | 42.9% | 46.8% | 49.8% |
| Currently Married | 41.0% | 45.1% | 48.0% |
| Married but Separated | 1.9% | 1.7% | 1.8% |
| Single Population | 57.1% | 53.2% | 50.2% |
| Never Married | 36.1% | 40.1% | 33.8% |
| Divorced | 14.9% | 8.4% | 10.8% |
| Widowed | 6.1% | 4.6% | 5.6% |
| space5 | | | |
| Household Size | 2.26 | 2.23 | 2.60 |
| Households | 111,860 | 44,515 | 124,010,992 |
| Family Households | 59,051 | 23,022 | 80,755,759 |
| Married couple, w/children | 23.4% | 31.0% | 30.5% |
| Married couple, no children | 48.1% | 44.5% | 42.9% |
| Non Family Households | 52,809 | 21,493 | 43,255,233 |
| Single householder, w/children | 15.7% | 11.1% | 15.8% |
| Single householder, no children | 12.9% | 13.4% | 10.8% |