| | Belleair Bluffs, FL | Marco Island, FL | United States |
| Population | 2,436 | 15,929 | 329,725,481 |
| Female Population | 53.0% | 50.1% | 50.5% |
| Male Population | 47.0% | 49.9% | 49.5% |
| Median Age | 60.1 | 66.9 | 38.4 |
| space3 | | | |
| Population - 2010 | 2,159 | 16,453 | 309,327,143 |
| Population - 2000 | 2,243 | 15,068 | 285,036,114 |
| Population - 1990 | 2,128 | 9,980 | 251,960,433 |
| Pop. 2000 to Now | -1.1% | 20.1% | 15.6% |
| Pop. 1990 to Now | 4.2% | 81.3% | 30.8% |
| space4 | | | |
| Population Density | 5,295.7 | 1,310.2 | 93.4 |
| Land Area | 0.5 | 12.2 | 3,531,905.4 |
| Water Area | 0.2 | 12.5 | 264,836.8 |
| space | | | |
| Est. Total Population By Age | | | |
| | Belleair Bluffs, FL | Marco Island, FL | United States |
| Age 0 to 4 | 3.2% | 1.0% | 5.9% |
| Age 5 to 9 | 3.5% | 2.1% | 6.1% |
| Age 10 to 14 | 4.2% | 2.9% | 6.6% |
| Age 15 to 17 | 2.7% | 1.5% | 3.9% |
| Age 18 to 20 | 0.2% | 0.7% | 4.0% |
| Age 21 to 24 | 1.2% | 2.0% | 5.2% |
| Age 25 to 34 | 5.1% | 3.4% | 13.8% |
| Age 35 to 44 | 7.1% | 4.2% | 12.9% |
| Age 45 to 54 | 13.6% | 8.1% | 12.6% |
| Age 55 to 59 | 8.9% | 7.4% | 6.7% |
| Age 60 to 64 | 16.1% | 9.7% | 6.3% |
| Age 65 to 74 | 21.5% | 25.6% | 9.6% |
| Age 75 to 84 | 9.6% | 23.8% | 4.5% |
| Age 85 and over | 3.0% | 7.8% | 1.9% |
| space1 | | | |
| Race | | | |
| | Belleair Bluffs, FL | Marco Island, FL | United States |
| White | 89.0% | 89.4% | 59.4% |
| Black | 2.7% | 0.4% | 12.2% |
| Asian | 2.5% | 0.8% | 5.6% |
| Native American | 0.1% | 0.0% | 0.6% |
| Hawaiian, Pacific Islander | 0.0% | 0.0% | 0.2% |
| Other | 0.0% | 0.0% | 0.4% |
| Two or More Races | 1.6% | 1.1% | 3.2% |
| Hispanic | 4.1% | 8.3% | 18.4% |
| space2 | | | |
| Marriage & Family | | | |
| | Belleair Bluffs, FL | Marco Island, FL | United States |
| Married Population | 56.6% | 75.5% | 49.8% |
| Currently Married | 55.5% | 74.7% | 48.0% |
| Married but Separated | 1.1% | 0.7% | 1.8% |
| Single Population | 43.4% | 24.5% | 50.2% |
| Never Married | 17.5% | 8.9% | 33.8% |
| Divorced | 17.1% | 6.7% | 10.8% |
| Widowed | 8.8% | 8.9% | 5.6% |
| space5 | | | |
| Household Size | 2.09 | 1.96 | 2.60 |
| Households | 1,168 | 8,131 | 124,010,992 |
| Family Households | 585 | 5,736 | 80,755,759 |
| Married couple, w/children | 14.0% | 9.3% | 30.5% |
| Married couple, no children | 65.8% | 86.1% | 42.9% |
| Non Family Households | 583 | 2,395 | 43,255,233 |
| Single householder, w/children | 14.2% | 1.5% | 15.8% |
| Single householder, no children | 6.0% | 3.1% | 10.8% |