| PEOPLE | Mercer Island | Mountain Brook | United States |
| Population | 22,699 | 20,413 | 308,035,306 |
| Pop. Density | 3,591 | 1,597 | 87 |
| Pop. Change | 4.32% | -1.28% | 8.07% |
| Median Age | 45.9 | 42 | 37.3 |
| Households | 9,109 | 7,731 | 116,716,292 |
| Household Size | 2.48 | 2.53 | 2.58 |
| Male Population | 48.66% | 47.73% | 49.27% |
| Female Population | 51.34% | 52.27% | 50.96% |
| Married Population | 64.67% | 60.07% | 47.02% |
| Single Population | 35.33% | 39.93% | 52.98% |
| ESTIMATED TOTAL POPULATION BY AGE | | | |
| Age 0 to 4 | 4.45% | 5.87% | 6.56% |
| Age 5 to 9 | 6.89% | 8.85% | 6.61% |
| Age 10 to 14 | 7.88% | 9.26% | 6.71% |
| Age 15 to 17 | 5.34% | 5.31% | 4.21% |
| Age 18 to 20 | 1.91% | 1.69% | 2.95% |
| Age 21 to 24 | 3.01% | 2.84% | 7.01% |
| Age 25 to 34 | 7.01% | 7.09% | 13.33% |
| Age 35 to 44 | 11.95% | 13.67% | 13.33% |
| Age 45 to 49 | 17.54% | 16.62% | 14.61% |
| Age 50 to 54 | 17.54% | 16.62% | 14.61% |
| Age 55 to 59 | 14.54% | 13.12% | 11.84% |
| Age 60 to 64 | 14.54% | 13.12% | 11.84% |
| Age 65 to 74 | 8.85% | 7.78% | 7.05% |
| Age 75 to 84 | 6.82% | 5.69% | 4.24% |
| Age 85 and over | 3.82% | 2.21% | 1.78% |
| RACE | | | |
| White | 77.88% | 97.23% | 72.41% |
| Black | 1.26% | 1.03% | 12.61% |
| Asian | 15.93% | 0.93% | 4.75% |
| American Indian | 0.22% | 0.06% | 0.95% |
| Other | 4.71% | 0.74% | 9.28% |
| Hispanic | 3.01% | 0.48% | 16.35% |
| Non-Hispanic | 96.99% | 99.52% | 83.65% |
| FAMILY | | | |
| Married, w/children | 37.89% | 43.89% | 30.42% |
| Married, no children | 48.93% | 46.08% | 42.46% |
| Single, w/children | 7.72% | 5.80% | 14.39% |
| Single, no children | 5.47% | 4.23% | 12.73% |
| Divorced | 8.60% | 8.04% | 10.62% |
| Separated | 3.78% | 1.20% | 4.97% |
| Widowed | 5.75% | 6.81% | 6.14% |
| Now Married | 63.47% | 60.11% | 46.32% |
| Never Married | 18.41% | 23.83% | 31.95% |
