| | Locust Valley, NY | Mill Valley, CA | United States |
| Population | 3,607 | 14,240 | 329,725,481 |
| Female Population | 47.0% | 52.5% | 50.5% |
| Male Population | 53.0% | 47.5% | 49.5% |
| Median Age | 41.5 | 47.9 | 38.4 |
| space3 | | | |
| Population - 2010 | 3,091 | 13,934 | 309,327,143 |
| Population - 2000 | 3,521 | 13,600 | 285,036,114 |
| Population - 1990 | 3,963 | 13,038 | 251,960,433 |
| Pop. 2000 to Now | -10.1% | 5.3% | 15.6% |
| Pop. 1990 to Now | -20.1% | 9.9% | 30.8% |
| space4 | | | |
| Population Density | 3,976.9 | 2,989.7 | 93.4 |
| Land Area | 0.9 | 4.8 | 3,531,905.4 |
| Water Area | 0.0 | 0.1 | 264,836.8 |
| space | | | |
| Est. Total Population By Age | | | |
| | Locust Valley, NY | Mill Valley, CA | United States |
| Age 0 to 4 | 5.9% | 2.9% | 5.9% |
| Age 5 to 9 | 6.5% | 5.8% | 6.1% |
| Age 10 to 14 | 11.4% | 6.3% | 6.6% |
| Age 15 to 17 | 4.5% | 6.1% | 3.9% |
| Age 18 to 20 | 4.3% | 3.4% | 4.0% |
| Age 21 to 24 | 2.4% | 1.5% | 5.2% |
| Age 25 to 34 | 7.8% | 7.3% | 13.8% |
| Age 35 to 44 | 12.4% | 12.2% | 12.9% |
| Age 45 to 54 | 19.1% | 18.4% | 12.6% |
| Age 55 to 59 | 4.5% | 7.8% | 6.7% |
| Age 60 to 64 | 8.2% | 7.1% | 6.3% |
| Age 65 to 74 | 7.5% | 11.6% | 9.6% |
| Age 75 to 84 | 2.2% | 6.5% | 4.5% |
| Age 85 and over | 3.4% | 3.0% | 1.9% |
| space1 | | | |
| Race | | | |
| | Locust Valley, NY | Mill Valley, CA | United States |
| White | 79.3% | 83.0% | 59.4% |
| Black | 1.5% | 1.4% | 12.2% |
| Asian | 0.7% | 6.1% | 5.6% |
| Native American | 0.0% | 0.0% | 0.6% |
| Hawaiian, Pacific Islander | 0.0% | 0.0% | 0.2% |
| Other | 0.0% | 1.0% | 0.4% |
| Two or More Races | 1.1% | 5.4% | 3.2% |
| Hispanic | 17.4% | 3.0% | 18.4% |
| space2 | | | |
| Marriage & Family | | | |
| | Locust Valley, NY | Mill Valley, CA | United States |
| Married Population | 62.0% | 56.1% | 49.8% |
| Currently Married | 61.4% | 55.6% | 48.0% |
| Married but Separated | 0.6% | 0.5% | 1.8% |
| Single Population | 38.0% | 43.9% | 50.2% |
| Never Married | 28.3% | 26.9% | 33.8% |
| Divorced | 6.1% | 12.5% | 10.8% |
| Widowed | 3.6% | 4.5% | 5.6% |
| space5 | | | |
| Household Size | 2.97 | 2.52 | 2.60 |
| Households | 1,209 | 5,622 | 124,010,992 |
| Family Households | 961 | 3,814 | 80,755,759 |
| Married couple, w/children | 35.5% | 35.2% | 30.5% |
| Married couple, no children | 50.1% | 49.5% | 42.9% |
| Non Family Households | 248 | 1,808 | 43,255,233 |
| Single householder, w/children | 9.7% | 9.8% | 15.8% |
| Single householder, no children | 4.8% | 5.6% | 10.8% |