| | Sammamish, WA | Belmont, CA | United States |
| Population | 66,532 | 28,109 | 329,725,481 |
| Female Population | 51.8% | 49.1% | 50.5% |
| Male Population | 48.2% | 50.9% | 49.5% |
| Median Age | 39.2 | 40.2 | 38.4 |
| space3 | | | |
| Population - 2010 | 57,656 | 25,933 | 309,327,143 |
| Population - 2000 | 34,104 | 25,123 | 285,036,114 |
| Population - 1990 | 23,294 | 24,127 | 251,960,433 |
| Pop. 2000 to Now | 93.4% | 5.6% | 15.6% |
| Pop. 1990 to Now | 183.2% | 10.0% | 30.8% |
| space4 | | | |
| Population Density | 3,255.5 | 6,065.8 | 93.4 |
| Land Area | 20.4 | 4.6 | 3,531,905.4 |
| Water Area | 3.7 | 0.0 | 264,836.8 |
| space | | | |
| Est. Total Population By Age | | | |
| | Sammamish, WA | Belmont, CA | United States |
| Age 0 to 4 | 6.1% | 6.0% | 5.9% |
| Age 5 to 9 | 7.3% | 6.3% | 6.1% |
| Age 10 to 14 | 9.9% | 6.5% | 6.6% |
| Age 15 to 17 | 6.3% | 4.7% | 3.9% |
| Age 18 to 20 | 2.7% | 2.5% | 4.0% |
| Age 21 to 24 | 2.9% | 2.4% | 5.2% |
| Age 25 to 34 | 8.0% | 12.7% | 13.8% |
| Age 35 to 44 | 18.2% | 16.5% | 12.9% |
| Age 45 to 54 | 19.1% | 14.8% | 12.6% |
| Age 55 to 59 | 6.5% | 7.3% | 6.7% |
| Age 60 to 64 | 5.3% | 5.6% | 6.3% |
| Age 65 to 74 | 5.6% | 8.1% | 9.6% |
| Age 75 to 84 | 1.7% | 4.0% | 4.5% |
| Age 85 and over | 0.5% | 2.6% | 1.9% |
| space1 | | | |
| Race | | | |
| | Sammamish, WA | Belmont, CA | United States |
| White | 55.8% | 49.1% | 59.4% |
| Black | 1.6% | 1.1% | 12.2% |
| Asian | 33.3% | 29.9% | 5.6% |
| Native American | 0.3% | 0.2% | 0.6% |
| Hawaiian, Pacific Islander | 0.1% | 1.4% | 0.2% |
| Other | 0.4% | 1.1% | 0.4% |
| Two or More Races | 4.9% | 5.3% | 3.2% |
| Hispanic | 3.5% | 12.1% | 18.4% |
| space2 | | | |
| Marriage & Family | | | |
| | Sammamish, WA | Belmont, CA | United States |
| Married Population | 70.7% | 62.1% | 49.8% |
| Currently Married | 70.0% | 60.8% | 48.0% |
| Married but Separated | 0.7% | 1.2% | 1.8% |
| Single Population | 29.3% | 37.9% | 50.2% |
| Never Married | 22.7% | 25.6% | 33.8% |
| Divorced | 4.8% | 8.6% | 10.8% |
| Widowed | 1.9% | 3.6% | 5.6% |
| space5 | | | |
| Household Size | 3.03 | 2.51 | 2.60 |
| Households | 21,930 | 10,961 | 124,010,992 |
| Family Households | 19,138 | 7,662 | 80,755,759 |
| Married couple, w/children | 54.5% | 44.3% | 30.5% |
| Married couple, no children | 34.7% | 43.9% | 42.9% |
| Non Family Households | 2,792 | 3,299 | 43,255,233 |
| Single householder, w/children | 7.1% | 7.6% | 15.8% |
| Single householder, no children | 3.7% | 4.3% | 10.8% |