| | Fernandina Beach, FL | St. Augustine Beach, FL | United States |
| Population | 12,697 | 6,688 | 329,725,481 |
| Female Population | 49.8% | 49.5% | 50.5% |
| Male Population | 50.3% | 50.5% | 49.5% |
| Median Age | 56.7 | 49.2 | 38.4 |
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| Population - 2010 | 11,377 | 6,184 | 309,327,143 |
| Population - 2000 | 10,549 | 4,683 | 285,036,114 |
| Population - 1990 | 8,765 | 3,657 | 251,960,433 |
| Pop. 2000 to Now | 26.0% | 52.4% | 15.6% |
| Pop. 1990 to Now | 51.6% | 95.2% | 30.8% |
| space4 | | | |
| Population Density | 1,109.9 | 3,162.2 | 93.4 |
| Land Area | 11.4 | 2.1 | 3,531,905.4 |
| Water Area | 0.7 | 0.1 | 264,836.8 |
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| Est. Total Population By Age | | | |
| | Fernandina Beach, FL | St. Augustine Beach, FL | United States |
| Age 0 to 4 | 4.0% | 2.8% | 5.9% |
| Age 5 to 9 | 2.5% | 3.3% | 6.1% |
| Age 10 to 14 | 2.6% | 7.0% | 6.6% |
| Age 15 to 17 | 1.7% | 3.8% | 3.9% |
| Age 18 to 20 | 2.9% | 3.6% | 4.0% |
| Age 21 to 24 | 2.9% | 5.5% | 5.2% |
| Age 25 to 34 | 8.9% | 2.5% | 13.8% |
| Age 35 to 44 | 8.4% | 16.7% | 12.9% |
| Age 45 to 54 | 13.6% | 11.7% | 12.6% |
| Age 55 to 59 | 9.5% | 7.5% | 6.7% |
| Age 60 to 64 | 9.6% | 12.7% | 6.3% |
| Age 65 to 74 | 20.5% | 14.2% | 9.6% |
| Age 75 to 84 | 11.0% | 6.8% | 4.5% |
| Age 85 and over | 2.0% | 1.9% | 1.9% |
| space1 | | | |
| Race | | | |
| | Fernandina Beach, FL | St. Augustine Beach, FL | United States |
| White | 74.1% | 94.3% | 59.4% |
| Black | 11.7% | 0.1% | 12.2% |
| Asian | 1.7% | 0.4% | 5.6% |
| Native American | 0.0% | 0.0% | 0.6% |
| Hawaiian, Pacific Islander | 0.0% | 0.0% | 0.2% |
| Other | 0.0% | 0.0% | 0.4% |
| Two or More Races | 0.6% | 1.2% | 3.2% |
| Hispanic | 11.9% | 4.0% | 18.4% |
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| Marriage & Family | | | |
| | Fernandina Beach, FL | St. Augustine Beach, FL | United States |
| Married Population | 53.2% | 52.4% | 49.8% |
| Currently Married | 52.4% | 51.7% | 48.0% |
| Married but Separated | 0.8% | 0.7% | 1.8% |
| Single Population | 46.8% | 47.6% | 50.2% |
| Never Married | 23.7% | 25.3% | 33.8% |
| Divorced | 13.5% | 14.2% | 10.8% |
| Widowed | 9.6% | 8.1% | 5.6% |
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| Household Size | 2.12 | 2.39 | 2.60 |
| Households | 5,869 | 2,799 | 124,010,992 |
| Family Households | 3,745 | 1,681 | 80,755,759 |
| Married couple, w/children | 11.8% | 28.7% | 30.5% |
| Married couple, no children | 62.8% | 55.3% | 42.9% |
| Non Family Households | 2,124 | 1,118 | 43,255,233 |
| Single householder, w/children | 6.9% | 6.9% | 15.8% |
| Single householder, no children | 18.5% | 9.0% | 10.8% |