| | Grass Valley, CA | Atwater, CA | United States |
| Population | 13,550 | 31,401 | 329,725,481 |
| Female Population | 55.1% | 49.7% | 50.5% |
| Male Population | 44.9% | 50.3% | 49.5% |
| Median Age | 47 | 34.1 | 38.4 |
| space3 | | | |
| Population - 2010 | 12,876 | 28,614 | 309,327,143 |
| Population - 2000 | 10,922 | 23,113 | 285,036,114 |
| Population - 1990 | 9,048 | 22,282 | 251,960,433 |
| Pop. 2000 to Now | 16.9% | 31.1% | 15.6% |
| Pop. 1990 to Now | 41.1% | 36.0% | 30.8% |
| space4 | | | |
| Population Density | 2,581.4 | 5,154.5 | 93.4 |
| Land Area | 5.2 | 6.1 | 3,531,905.4 |
| Water Area | 0.0 | 0.0 | 264,836.8 |
| space | | | |
| Est. Total Population By Age | | | |
| | Grass Valley, CA | Atwater, CA | United States |
| Age 0 to 4 | 6.0% | 6.0% | 5.9% |
| Age 5 to 9 | 5.3% | 7.9% | 6.1% |
| Age 10 to 14 | 7.4% | 9.4% | 6.6% |
| Age 15 to 17 | 1.6% | 4.9% | 3.9% |
| Age 18 to 20 | 1.0% | 3.7% | 4.0% |
| Age 21 to 24 | 4.2% | 5.3% | 5.2% |
| Age 25 to 34 | 9.9% | 13.9% | 13.8% |
| Age 35 to 44 | 12.5% | 13.6% | 12.9% |
| Age 45 to 54 | 9.6% | 11.7% | 12.6% |
| Age 55 to 59 | 6.6% | 6.1% | 6.7% |
| Age 60 to 64 | 7.3% | 5.0% | 6.3% |
| Age 65 to 74 | 13.9% | 6.6% | 9.6% |
| Age 75 to 84 | 7.2% | 4.1% | 4.5% |
| Age 85 and over | 7.6% | 1.8% | 1.9% |
| space1 | | | |
| Race | | | |
| | Grass Valley, CA | Atwater, CA | United States |
| White | 78.6% | 31.9% | 59.4% |
| Black | 0.5% | 3.9% | 12.2% |
| Asian | 1.7% | 5.0% | 5.6% |
| Native American | 0.0% | 0.1% | 0.6% |
| Hawaiian, Pacific Islander | 0.0% | 0.8% | 0.2% |
| Other | 0.2% | 0.4% | 0.4% |
| Two or More Races | 8.0% | 2.6% | 3.2% |
| Hispanic | 11.0% | 55.3% | 18.4% |
| space2 | | | |
| Marriage & Family | | | |
| | Grass Valley, CA | Atwater, CA | United States |
| Married Population | 35.2% | 51.8% | 49.8% |
| Currently Married | 32.9% | 47.8% | 48.0% |
| Married but Separated | 2.3% | 3.9% | 1.8% |
| Single Population | 64.8% | 48.2% | 50.2% |
| Never Married | 28.3% | 32.4% | 33.8% |
| Divorced | 22.3% | 9.2% | 10.8% |
| Widowed | 14.3% | 6.7% | 5.6% |
| space5 | | | |
| Household Size | 1.99 | 3.03 | 2.60 |
| Households | 6,495 | 10,309 | 124,010,992 |
| Family Households | 2,890 | 7,783 | 80,755,759 |
| Married couple, w/children | 24.8% | 30.9% | 30.5% |
| Married couple, no children | 33.7% | 34.6% | 42.9% |
| Non Family Households | 3,605 | 2,526 | 43,255,233 |
| Single householder, w/children | 24.9% | 22.1% | 15.8% |
| Single householder, no children | 16.6% | 12.5% | 10.8% |