| | St. James City, FL | Marco Island, FL | United States |
| Population | 3,551 | 15,929 | 329,725,481 |
| Female Population | 46.3% | 50.1% | 50.5% |
| Male Population | 53.7% | 49.9% | 49.5% |
| Median Age | 63.7 | 66.9 | 38.4 |
| space3 | | | |
| Population - 2010 | 3,347 | 16,453 | 309,327,143 |
| Population - 2000 | 4,105 | 15,068 | 285,036,114 |
| Population - 1990 | 1,904 | 9,980 | 251,960,433 |
| Pop. 2000 to Now | 1.0% | 20.1% | 15.6% |
| Pop. 1990 to Now | 117.8% | 81.3% | 30.8% |
| space4 | | | |
| Population Density | 243.1 | 1,310.2 | 93.4 |
| Land Area | 14.6 | 12.2 | 3,531,905.4 |
| Water Area | 2.1 | 12.5 | 264,836.8 |
| space | | | |
| Est. Total Population By Age | | | |
| | St. James City, FL | Marco Island, FL | United States |
| Age 0 to 4 | 0.0% | 1.0% | 5.9% |
| Age 5 to 9 | 3.9% | 2.1% | 6.1% |
| Age 10 to 14 | 1.2% | 2.9% | 6.6% |
| Age 15 to 17 | 1.4% | 1.5% | 3.9% |
| Age 18 to 20 | 1.0% | 0.7% | 4.0% |
| Age 21 to 24 | 1.2% | 2.0% | 5.2% |
| Age 25 to 34 | 5.5% | 3.4% | 13.8% |
| Age 35 to 44 | 1.0% | 4.2% | 12.9% |
| Age 45 to 54 | 18.6% | 8.1% | 12.6% |
| Age 55 to 59 | 9.2% | 7.4% | 6.7% |
| Age 60 to 64 | 12.2% | 9.7% | 6.3% |
| Age 65 to 74 | 29.0% | 25.6% | 9.6% |
| Age 75 to 84 | 12.1% | 23.8% | 4.5% |
| Age 85 and over | 3.9% | 7.8% | 1.9% |
| space1 | | | |
| Race | | | |
| | St. James City, FL | Marco Island, FL | United States |
| White | 96.1% | 89.4% | 59.4% |
| Black | 0.0% | 0.4% | 12.2% |
| Asian | 0.4% | 0.8% | 5.6% |
| Native American | 0.0% | 0.0% | 0.6% |
| Hawaiian, Pacific Islander | 1.0% | 0.0% | 0.2% |
| Other | 0.0% | 0.0% | 0.4% |
| Two or More Races | 1.0% | 1.1% | 3.2% |
| Hispanic | 1.5% | 8.3% | 18.4% |
| space2 | | | |
| Marriage & Family | | | |
| | St. James City, FL | Marco Island, FL | United States |
| Married Population | 61.8% | 75.5% | 49.8% |
| Currently Married | 61.4% | 74.7% | 48.0% |
| Married but Separated | 0.4% | 0.7% | 1.8% |
| Single Population | 38.2% | 24.5% | 50.2% |
| Never Married | 13.9% | 8.9% | 33.8% |
| Divorced | 15.2% | 6.7% | 10.8% |
| Widowed | 9.1% | 8.9% | 5.6% |
| space5 | | | |
| Household Size | 2.07 | 1.96 | 2.60 |
| Households | 1,719 | 8,131 | 124,010,992 |
| Family Households | 1,129 | 5,736 | 80,755,759 |
| Married couple, w/children | 11.3% | 9.3% | 30.5% |
| Married couple, no children | 76.0% | 86.1% | 42.9% |
| Non Family Households | 590 | 2,395 | 43,255,233 |
| Single householder, w/children | 5.1% | 1.5% | 15.8% |
| Single householder, no children | 7.5% | 3.1% | 10.8% |