| | Hercules, CA | Vallejo, CA | United States |
| Population | 26,050 | 125,350 | 329,725,481 |
| Female Population | 51.8% | 51.2% | 50.5% |
| Male Population | 48.2% | 48.8% | 49.5% |
| Median Age | 42.7 | 39.8 | 38.4 |
| space3 | | | |
| Population - 2010 | 24,140 | 116,118 | 309,327,143 |
| Population - 2000 | 19,488 | 116,760 | 285,036,114 |
| Population - 1990 | 16,829 | 109,199 | 251,960,433 |
| Pop. 2000 to Now | 34.6% | 3.4% | 15.6% |
| Pop. 1990 to Now | 55.8% | 10.6% | 30.8% |
| space4 | | | |
| Population Density | 4,064.0 | 4,084.1 | 93.4 |
| Land Area | 6.4 | 30.7 | 3,531,905.4 |
| Water Area | 13.6 | 18.9 | 264,836.8 |
| space | | | |
| Est. Total Population By Age | | | |
| | Hercules, CA | Vallejo, CA | United States |
| Age 0 to 4 | 3.9% | 5.2% | 5.9% |
| Age 5 to 9 | 6.3% | 5.9% | 6.1% |
| Age 10 to 14 | 6.6% | 6.3% | 6.6% |
| Age 15 to 17 | 2.8% | 3.6% | 3.9% |
| Age 18 to 20 | 3.1% | 3.4% | 4.0% |
| Age 21 to 24 | 4.4% | 5.4% | 5.2% |
| Age 25 to 34 | 11.8% | 14.0% | 13.8% |
| Age 35 to 44 | 14.2% | 13.5% | 12.9% |
| Age 45 to 54 | 12.5% | 12.4% | 12.6% |
| Age 55 to 59 | 8.6% | 6.7% | 6.7% |
| Age 60 to 64 | 8.0% | 7.4% | 6.3% |
| Age 65 to 74 | 11.9% | 10.4% | 9.6% |
| Age 75 to 84 | 4.7% | 4.2% | 4.5% |
| Age 85 and over | 1.2% | 1.7% | 1.9% |
| space1 | | | |
| Race | | | |
| | Hercules, CA | Vallejo, CA | United States |
| White | 18.0% | 23.5% | 59.4% |
| Black | 17.2% | 17.5% | 12.2% |
| Asian | 42.3% | 22.6% | 5.6% |
| Native American | 0.1% | 0.2% | 0.6% |
| Hawaiian, Pacific Islander | 1.3% | 0.7% | 0.2% |
| Other | 0.2% | 1.2% | 0.4% |
| Two or More Races | 4.9% | 5.4% | 3.2% |
| Hispanic | 16.0% | 28.8% | 18.4% |
| space2 | | | |
| Marriage & Family | | | |
| | Hercules, CA | Vallejo, CA | United States |
| Married Population | 55.4% | 46.7% | 49.8% |
| Currently Married | 53.7% | 44.5% | 48.0% |
| Married but Separated | 1.7% | 2.2% | 1.8% |
| Single Population | 44.6% | 53.3% | 50.2% |
| Never Married | 31.3% | 36.6% | 33.8% |
| Divorced | 9.5% | 11.2% | 10.8% |
| Widowed | 3.8% | 5.5% | 5.6% |
| space5 | | | |
| Household Size | 2.87 | 2.82 | 2.60 |
| Households | 9,068 | 43,883 | 124,010,992 |
| Family Households | 6,650 | 29,561 | 80,755,759 |
| Married couple, w/children | 30.7% | 27.9% | 30.5% |
| Married couple, no children | 44.6% | 38.5% | 42.9% |
| Non Family Households | 2,418 | 14,322 | 43,255,233 |
| Single householder, w/children | 12.4% | 20.1% | 15.8% |
| Single householder, no children | 12.2% | 13.5% | 10.8% |