| | St. Augustine, FL | Decatur, GA | United States |
| Population | 13,994 | 24,334 | 329,725,481 |
| Female Population | 56.3% | 52.6% | 50.5% |
| Male Population | 43.7% | 47.4% | 49.5% |
| Median Age | 46.2 | 38.6 | 38.4 |
| space3 | | | |
| Population - 2010 | 13,062 | 19,700 | 309,327,143 |
| Population - 2000 | 11,592 | 18,147 | 285,036,114 |
| Population - 1990 | 11,692 | 17,336 | 251,960,433 |
| Pop. 2000 to Now | 42.5% | 41.4% | 15.6% |
| Pop. 1990 to Now | 41.3% | 48.0% | 30.8% |
| space4 | | | |
| Population Density | 1,480.7 | 5,485.6 | 93.4 |
| Land Area | 9.5 | 4.4 | 3,531,905.4 |
| Water Area | 3.3 | 0.0 | 264,836.8 |
| space | | | |
| Est. Total Population By Age | | | |
| | St. Augustine, FL | Decatur, GA | United States |
| Age 0 to 4 | 1.3% | 6.9% | 5.9% |
| Age 5 to 9 | 3.5% | 10.7% | 6.1% |
| Age 10 to 14 | 2.1% | 10.2% | 6.6% |
| Age 15 to 17 | 1.9% | 4.4% | 3.9% |
| Age 18 to 20 | 11.0% | 3.3% | 4.0% |
| Age 21 to 24 | 4.7% | 2.4% | 5.2% |
| Age 25 to 34 | 13.8% | 7.6% | 13.8% |
| Age 35 to 44 | 9.9% | 15.3% | 12.9% |
| Age 45 to 54 | 10.3% | 16.0% | 12.6% |
| Age 55 to 59 | 7.1% | 6.5% | 6.7% |
| Age 60 to 64 | 7.7% | 5.3% | 6.3% |
| Age 65 to 74 | 16.5% | 6.9% | 9.6% |
| Age 75 to 84 | 5.9% | 3.0% | 4.5% |
| Age 85 and over | 4.3% | 1.6% | 1.9% |
| space1 | | | |
| Race | | | |
| | St. Augustine, FL | Decatur, GA | United States |
| White | 81.2% | 66.9% | 59.4% |
| Black | 6.3% | 15.6% | 12.2% |
| Asian | 1.4% | 3.9% | 5.6% |
| Native American | 0.1% | 0.4% | 0.6% |
| Hawaiian, Pacific Islander | 0.1% | 0.0% | 0.2% |
| Other | 0.0% | 0.0% | 0.4% |
| Two or More Races | 3.5% | 6.5% | 3.2% |
| Hispanic | 7.5% | 6.9% | 18.4% |
| space2 | | | |
| Marriage & Family | | | |
| | St. Augustine, FL | Decatur, GA | United States |
| Married Population | 37.6% | 58.3% | 49.8% |
| Currently Married | 36.2% | 56.7% | 48.0% |
| Married but Separated | 1.4% | 1.6% | 1.8% |
| Single Population | 62.4% | 41.7% | 50.2% |
| Never Married | 42.2% | 27.6% | 33.8% |
| Divorced | 12.5% | 9.6% | 10.8% |
| Widowed | 7.6% | 4.6% | 5.6% |
| space5 | | | |
| Household Size | 2.30 | 2.64 | 2.60 |
| Households | 5,538 | 8,906 | 124,010,992 |
| Family Households | 2,726 | 5,849 | 80,755,759 |
| Married couple, w/children | 13.0% | 52.8% | 30.5% |
| Married couple, no children | 65.6% | 31.0% | 42.9% |
| Non Family Households | 2,812 | 3,057 | 43,255,233 |
| Single householder, w/children | 9.0% | 12.1% | 15.8% |
| Single householder, no children | 12.4% | 4.2% | 10.8% |