| | Del Mar, CA | Atherton, CA | United States |
| Population | 4,008 | 7,181 | 329,725,481 |
| Female Population | 52.4% | 50.1% | 50.5% |
| Male Population | 47.6% | 49.9% | 49.5% |
| Median Age | 50.5 | 47.9 | 38.4 |
| space3 | | | |
| Population - 2010 | 4,172 | 6,932 | 309,327,143 |
| Population - 2000 | 4,389 | 7,194 | 285,036,114 |
| Population - 1990 | 4,860 | 7,163 | 251,960,433 |
| Pop. 2000 to Now | -1.9% | -2.5% | 15.6% |
| Pop. 1990 to Now | -11.4% | -2.1% | 30.8% |
| space4 | | | |
| Population Density | 2,348.0 | 1,427.6 | 93.4 |
| Land Area | 1.7 | 5.0 | 3,531,905.4 |
| Water Area | 0.1 | 0.0 | 264,836.8 |
| space | | | |
| Est. Total Population By Age | | | |
| | Del Mar, CA | Atherton, CA | United States |
| Age 0 to 4 | 2.6% | 2.1% | 5.9% |
| Age 5 to 9 | 3.5% | 3.3% | 6.1% |
| Age 10 to 14 | 6.0% | 9.1% | 6.6% |
| Age 15 to 17 | 1.8% | 5.9% | 3.9% |
| Age 18 to 20 | 0.5% | 8.4% | 4.0% |
| Age 21 to 24 | 2.0% | 4.5% | 5.2% |
| Age 25 to 34 | 10.9% | 7.1% | 13.8% |
| Age 35 to 44 | 8.2% | 6.8% | 12.9% |
| Age 45 to 54 | 19.5% | 15.3% | 12.6% |
| Age 55 to 59 | 11.1% | 7.9% | 6.7% |
| Age 60 to 64 | 3.5% | 5.7% | 6.3% |
| Age 65 to 74 | 19.6% | 12.6% | 9.6% |
| Age 75 to 84 | 8.9% | 6.9% | 4.5% |
| Age 85 and over | 2.0% | 4.5% | 1.9% |
| space1 | | | |
| Race | | | |
| | Del Mar, CA | Atherton, CA | United States |
| White | 83.2% | 67.9% | 59.4% |
| Black | 2.7% | 1.2% | 12.2% |
| Asian | 0.3% | 18.6% | 5.6% |
| Native American | 0.0% | 0.1% | 0.6% |
| Hawaiian, Pacific Islander | 0.0% | 0.4% | 0.2% |
| Other | 0.0% | 0.0% | 0.4% |
| Two or More Races | 4.0% | 3.1% | 3.2% |
| Hispanic | 9.6% | 8.8% | 18.4% |
| space2 | | | |
| Marriage & Family | | | |
| | Del Mar, CA | Atherton, CA | United States |
| Married Population | 65.9% | 58.9% | 49.8% |
| Currently Married | 64.3% | 58.3% | 48.0% |
| Married but Separated | 1.6% | 0.6% | 1.8% |
| Single Population | 34.1% | 41.1% | 50.2% |
| Never Married | 21.2% | 33.3% | 33.8% |
| Divorced | 11.2% | 3.4% | 10.8% |
| Widowed | 1.7% | 4.4% | 5.6% |
| space5 | | | |
| Household Size | 2.20 | 2.92 | 2.60 |
| Households | 1,818 | 2,244 | 124,010,992 |
| Family Households | 1,214 | 1,843 | 80,755,759 |
| Married couple, w/children | 20.3% | 35.7% | 30.5% |
| Married couple, no children | 70.3% | 55.9% | 42.9% |
| Non Family Households | 604 | 401 | 43,255,233 |
| Single householder, w/children | 7.7% | 5.1% | 15.8% |
| Single householder, no children | 1.8% | 3.3% | 10.8% |