| | Sebastian, FL | Irvine, CA | United States |
| Population | 24,843 | 297,868 | 329,725,481 |
| Female Population | 50.8% | 50.8% | 50.5% |
| Male Population | 49.2% | 49.3% | 49.5% |
| Median Age | 56.7 | 33.8 | 38.4 |
| space3 | | | |
| Population - 2010 | 21,971 | 214,371 | 309,327,143 |
| Population - 2000 | 16,181 | 143,072 | 285,036,114 |
| Population - 1990 | 10,205 | 110,330 | 251,960,433 |
| Pop. 2000 to Now | 63.7% | 98.3% | 15.6% |
| Pop. 1990 to Now | 159.5% | 157.1% | 30.8% |
| space4 | | | |
| Population Density | 1,827.8 | 4,541.9 | 93.4 |
| Land Area | 13.6 | 65.6 | 3,531,905.4 |
| Water Area | 0.8 | 0.3 | 264,836.8 |
| space | | | |
| Est. Total Population By Age | | | |
| | Sebastian, FL | Irvine, CA | United States |
| Age 0 to 4 | 2.8% | 6.7% | 5.9% |
| Age 5 to 9 | 3.6% | 5.7% | 6.1% |
| Age 10 to 14 | 4.1% | 6.1% | 6.6% |
| Age 15 to 17 | 2.6% | 3.8% | 3.9% |
| Age 18 to 20 | 1.3% | 6.1% | 4.0% |
| Age 21 to 24 | 3.1% | 6.2% | 5.2% |
| Age 25 to 34 | 8.4% | 17.4% | 13.8% |
| Age 35 to 44 | 8.1% | 14.5% | 12.9% |
| Age 45 to 54 | 13.6% | 13.6% | 12.6% |
| Age 55 to 59 | 9.0% | 5.5% | 6.7% |
| Age 60 to 64 | 8.8% | 4.2% | 6.3% |
| Age 65 to 74 | 19.2% | 6.1% | 9.6% |
| Age 75 to 84 | 11.8% | 2.8% | 4.5% |
| Age 85 and over | 3.8% | 1.2% | 1.9% |
| space1 | | | |
| Race | | | |
| | Sebastian, FL | Irvine, CA | United States |
| White | 87.0% | 37.4% | 59.4% |
| Black | 1.7% | 1.7% | 12.2% |
| Asian | 0.5% | 42.6% | 5.6% |
| Native American | 0.3% | 0.1% | 0.6% |
| Hawaiian, Pacific Islander | 0.4% | 0.3% | 0.2% |
| Other | 0.7% | 0.3% | 0.4% |
| Two or More Races | 2.3% | 5.6% | 3.2% |
| Hispanic | 7.1% | 11.9% | 18.4% |
| space2 | | | |
| Marriage & Family | | | |
| | Sebastian, FL | Irvine, CA | United States |
| Married Population | 58.2% | 51.4% | 49.8% |
| Currently Married | 57.4% | 50.3% | 48.0% |
| Married but Separated | 0.8% | 1.1% | 1.8% |
| Single Population | 41.8% | 48.6% | 50.2% |
| Never Married | 19.7% | 38.4% | 33.8% |
| Divorced | 12.9% | 7.5% | 10.8% |
| Widowed | 9.2% | 2.7% | 5.6% |
| space5 | | | |
| Household Size | 2.33 | 2.70 | 2.60 |
| Households | 10,659 | 107,166 | 124,010,992 |
| Family Households | 6,813 | 69,181 | 80,755,759 |
| Married couple, w/children | 15.6% | 42.3% | 30.5% |
| Married couple, no children | 70.9% | 37.7% | 42.9% |
| Non Family Households | 3,846 | 37,985 | 43,255,233 |
| Single householder, w/children | 6.1% | 9.8% | 15.8% |
| Single householder, no children | 7.4% | 10.2% | 10.8% |