| | Union City, CA | Sunnyvale, CA | United States |
| Population | 70,828 | 155,550 | 329,725,481 |
| Female Population | 48.9% | 47.8% | 50.5% |
| Male Population | 51.1% | 52.2% | 49.5% |
| Median Age | 40.8 | 35.2 | 38.4 |
| space3 | | | |
| Population - 2010 | 69,628 | 140,786 | 309,327,143 |
| Population - 2000 | 66,869 | 131,760 | 285,036,114 |
| Population - 1990 | 53,762 | 117,229 | 251,960,433 |
| Pop. 2000 to Now | 11.4% | 15.2% | 15.6% |
| Pop. 1990 to Now | 38.6% | 29.4% | 30.8% |
| space4 | | | |
| Population Density | 3,650.9 | 7,073.0 | 93.4 |
| Land Area | 19.4 | 22.0 | 3,531,905.4 |
| Water Area | 0.0 | 0.7 | 264,836.8 |
| space | | | |
| Est. Total Population By Age | | | |
| | Union City, CA | Sunnyvale, CA | United States |
| Age 0 to 4 | 4.6% | 7.0% | 5.9% |
| Age 5 to 9 | 5.0% | 5.9% | 6.1% |
| Age 10 to 14 | 5.6% | 5.4% | 6.6% |
| Age 15 to 17 | 3.0% | 2.7% | 3.9% |
| Age 18 to 20 | 3.0% | 1.7% | 4.0% |
| Age 21 to 24 | 4.9% | 4.1% | 5.2% |
| Age 25 to 34 | 14.9% | 23.1% | 13.8% |
| Age 35 to 44 | 14.8% | 15.9% | 12.9% |
| Age 45 to 54 | 13.7% | 11.9% | 12.6% |
| Age 55 to 59 | 7.0% | 5.9% | 6.7% |
| Age 60 to 64 | 6.8% | 4.8% | 6.3% |
| Age 65 to 74 | 9.9% | 6.5% | 9.6% |
| Age 75 to 84 | 4.6% | 3.4% | 4.5% |
| Age 85 and over | 2.2% | 2.0% | 1.9% |
| space1 | | | |
| Race | | | |
| | Union City, CA | Sunnyvale, CA | United States |
| White | 14.7% | 28.9% | 59.4% |
| Black | 4.7% | 1.3% | 12.2% |
| Asian | 55.0% | 47.8% | 5.6% |
| Native American | 0.3% | 0.2% | 0.6% |
| Hawaiian, Pacific Islander | 0.9% | 0.1% | 0.2% |
| Other | 0.2% | 0.4% | 0.4% |
| Two or More Races | 3.8% | 4.5% | 3.2% |
| Hispanic | 20.3% | 16.8% | 18.4% |
| space2 | | | |
| Marriage & Family | | | |
| | Union City, CA | Sunnyvale, CA | United States |
| Married Population | 57.2% | 57.1% | 49.8% |
| Currently Married | 56.1% | 56.0% | 48.0% |
| Married but Separated | 1.1% | 1.1% | 1.8% |
| Single Population | 42.8% | 42.9% | 50.2% |
| Never Married | 31.3% | 33.1% | 33.8% |
| Divorced | 6.4% | 6.1% | 10.8% |
| Widowed | 5.1% | 3.7% | 5.6% |
| space5 | | | |
| Household Size | 3.37 | 2.69 | 2.60 |
| Households | 20,800 | 57,565 | 124,010,992 |
| Family Households | 16,979 | 37,930 | 80,755,759 |
| Married couple, w/children | 35.0% | 41.3% | 30.5% |
| Married couple, no children | 46.1% | 41.3% | 42.9% |
| Non Family Households | 3,821 | 19,635 | 43,255,233 |
| Single householder, w/children | 7.9% | 8.0% | 15.8% |
| Single householder, no children | 11.1% | 9.4% | 10.8% |