| | Siesta Key, FL | Fernandina Beach, FL | United States |
| Population | 5,416 | 12,697 | 329,725,481 |
| Female Population | 51.2% | 49.8% | 50.5% |
| Male Population | 48.8% | 50.3% | 49.5% |
| Median Age | 67.1 | 56.7 | 38.4 |
| space3 | | | |
| Population - 2010 | 6,573 | 11,377 | 309,327,143 |
| Population - 2000 | 7,150 | 10,549 | 285,036,114 |
| Population - 1990 | 7,772 | 8,765 | 251,960,433 |
| Pop. 2000 to Now | -10.4% | 26.0% | 15.6% |
| Pop. 1990 to Now | -17.6% | 51.6% | 30.8% |
| space4 | | | |
| Population Density | 2,311.6 | 1,109.9 | 93.4 |
| Land Area | 2.3 | 11.4 | 3,531,905.4 |
| Water Area | 1.1 | 0.7 | 264,836.8 |
| space | | | |
| Est. Total Population By Age | | | |
| | Siesta Key, FL | Fernandina Beach, FL | United States |
| Age 0 to 4 | 1.0% | 4.0% | 5.9% |
| Age 5 to 9 | 0.5% | 2.5% | 6.1% |
| Age 10 to 14 | 2.2% | 2.6% | 6.6% |
| Age 15 to 17 | 2.7% | 1.7% | 3.9% |
| Age 18 to 20 | 0.6% | 2.9% | 4.0% |
| Age 21 to 24 | 2.1% | 2.9% | 5.2% |
| Age 25 to 34 | 3.0% | 8.9% | 13.8% |
| Age 35 to 44 | 3.3% | 8.4% | 12.9% |
| Age 45 to 54 | 8.4% | 13.6% | 12.6% |
| Age 55 to 59 | 10.3% | 9.5% | 6.7% |
| Age 60 to 64 | 11.0% | 9.6% | 6.3% |
| Age 65 to 74 | 24.9% | 20.5% | 9.6% |
| Age 75 to 84 | 22.9% | 11.0% | 4.5% |
| Age 85 and over | 7.1% | 2.0% | 1.9% |
| space1 | | | |
| Race | | | |
| | Siesta Key, FL | Fernandina Beach, FL | United States |
| White | 92.9% | 74.1% | 59.4% |
| Black | 0.0% | 11.7% | 12.2% |
| Asian | 1.8% | 1.7% | 5.6% |
| Native American | 0.4% | 0.0% | 0.6% |
| Hawaiian, Pacific Islander | 0.0% | 0.0% | 0.2% |
| Other | 0.4% | 0.0% | 0.4% |
| Two or More Races | 1.8% | 0.6% | 3.2% |
| Hispanic | 2.7% | 11.9% | 18.4% |
| space2 | | | |
| Marriage & Family | | | |
| | Siesta Key, FL | Fernandina Beach, FL | United States |
| Married Population | 66.0% | 53.2% | 49.8% |
| Currently Married | 65.3% | 52.4% | 48.0% |
| Married but Separated | 0.8% | 0.8% | 1.8% |
| Single Population | 34.0% | 46.8% | 50.2% |
| Never Married | 11.5% | 23.7% | 33.8% |
| Divorced | 11.8% | 13.5% | 10.8% |
| Widowed | 10.6% | 9.6% | 5.6% |
| space5 | | | |
| Household Size | 1.84 | 2.12 | 2.60 |
| Households | 2,948 | 5,869 | 124,010,992 |
| Family Households | 1,788 | 3,745 | 80,755,759 |
| Married couple, w/children | 7.6% | 11.8% | 30.5% |
| Married couple, no children | 84.8% | 62.8% | 42.9% |
| Non Family Households | 1,160 | 2,124 | 43,255,233 |
| Single householder, w/children | 3.1% | 6.9% | 15.8% |
| Single householder, no children | 4.4% | 18.5% | 10.8% |