| | St. Simons, GA | Marietta, GA | United States |
| Population | 15,865 | 60,962 | 329,725,481 |
| Female Population | 52.6% | 50.5% | 50.5% |
| Male Population | 47.5% | 49.5% | 49.5% |
| Median Age | 56.1 | 34.6 | 38.4 |
| space3 | | | |
| Population - 2010 | 12,854 | 56,593 | 309,327,143 |
| Population - 2000 | 13,381 | 58,748 | 285,036,114 |
| Population - 1990 | 12,124 | 44,129 | 251,960,433 |
| Pop. 2000 to Now | 9.4% | 3.5% | 15.6% |
| Pop. 1990 to Now | 20.7% | 37.8% | 30.8% |
| space4 | | | |
| Population Density | 962.6 | 2,611.8 | 93.4 |
| Land Area | 16.5 | 23.3 | 3,531,905.4 |
| Water Area | 1.0 | 0.1 | 264,836.8 |
| space | | | |
| Est. Total Population By Age | | | |
| | St. Simons, GA | Marietta, GA | United States |
| Age 0 to 4 | 4.3% | 5.9% | 5.9% |
| Age 5 to 9 | 4.0% | 6.1% | 6.1% |
| Age 10 to 14 | 2.3% | 6.2% | 6.6% |
| Age 15 to 17 | 3.3% | 3.0% | 3.9% |
| Age 18 to 20 | 1.0% | 6.0% | 4.0% |
| Age 21 to 24 | 2.4% | 6.6% | 5.2% |
| Age 25 to 34 | 8.2% | 17.0% | 13.8% |
| Age 35 to 44 | 8.9% | 14.5% | 12.9% |
| Age 45 to 54 | 14.4% | 10.2% | 12.6% |
| Age 55 to 59 | 7.2% | 5.4% | 6.7% |
| Age 60 to 64 | 8.6% | 5.6% | 6.3% |
| Age 65 to 74 | 22.6% | 8.1% | 9.6% |
| Age 75 to 84 | 9.0% | 2.9% | 4.5% |
| Age 85 and over | 3.8% | 2.4% | 1.9% |
| space1 | | | |
| Race | | | |
| | St. Simons, GA | Marietta, GA | United States |
| White | 93.6% | 45.3% | 59.4% |
| Black | 2.0% | 31.6% | 12.2% |
| Asian | 0.6% | 2.1% | 5.6% |
| Native American | 0.5% | 0.3% | 0.6% |
| Hawaiian, Pacific Islander | 0.0% | 0.0% | 0.2% |
| Other | 0.0% | 0.6% | 0.4% |
| Two or More Races | 1.5% | 3.8% | 3.2% |
| Hispanic | 1.9% | 16.3% | 18.4% |
| space2 | | | |
| Marriage & Family | | | |
| | St. Simons, GA | Marietta, GA | United States |
| Married Population | 64.3% | 40.0% | 49.8% |
| Currently Married | 63.6% | 37.4% | 48.0% |
| Married but Separated | 0.7% | 2.6% | 1.8% |
| Single Population | 35.7% | 60.0% | 50.2% |
| Never Married | 16.8% | 41.6% | 33.8% |
| Divorced | 11.2% | 13.9% | 10.8% |
| Widowed | 7.7% | 4.5% | 5.6% |
| space5 | | | |
| Household Size | 2.19 | 2.37 | 2.60 |
| Households | 7,163 | 24,400 | 124,010,992 |
| Family Households | 4,796 | 13,375 | 80,755,759 |
| Married couple, w/children | 20.9% | 25.5% | 30.5% |
| Married couple, no children | 70.7% | 40.1% | 42.9% |
| Non Family Households | 2,367 | 11,025 | 43,255,233 |
| Single householder, w/children | 2.9% | 21.6% | 15.8% |
| Single householder, no children | 5.5% | 12.8% | 10.8% |