| | Rockford, IL | Grass Valley, CA | United States |
| Population | 148,942 | 13,550 | 329,725,481 |
| Female Population | 51.1% | 55.1% | 50.5% |
| Male Population | 48.9% | 44.9% | 49.5% |
| Median Age | 37.6 | 47 | 38.4 |
| space3 | | | |
| Population - 2010 | 153,173 | 12,876 | 309,327,143 |
| Population - 2000 | 150,115 | 10,922 | 285,036,114 |
| Population - 1990 | 139,426 | 9,048 | 251,960,433 |
| Pop. 2000 to Now | -3.5% | 16.9% | 15.6% |
| Pop. 1990 to Now | 3.9% | 41.1% | 30.8% |
| space4 | | | |
| Population Density | 2,313.9 | 2,581.4 | 93.4 |
| Land Area | 64.4 | 5.2 | 3,531,905.4 |
| Water Area | 1.0 | 0.0 | 264,836.8 |
| space | | | |
| Est. Total Population By Age | | | |
| | Rockford, IL | Grass Valley, CA | United States |
| Age 0 to 4 | 6.8% | 6.0% | 5.9% |
| Age 5 to 9 | 6.8% | 5.3% | 6.1% |
| Age 10 to 14 | 7.3% | 7.4% | 6.6% |
| Age 15 to 17 | 4.1% | 1.6% | 3.9% |
| Age 18 to 20 | 3.2% | 1.0% | 4.0% |
| Age 21 to 24 | 5.3% | 4.2% | 5.2% |
| Age 25 to 34 | 13.3% | 9.9% | 13.8% |
| Age 35 to 44 | 11.9% | 12.5% | 12.9% |
| Age 45 to 54 | 11.7% | 9.6% | 12.6% |
| Age 55 to 59 | 6.6% | 6.6% | 6.7% |
| Age 60 to 64 | 6.2% | 7.3% | 6.3% |
| Age 65 to 74 | 9.5% | 13.9% | 9.6% |
| Age 75 to 84 | 4.1% | 7.2% | 4.5% |
| Age 85 and over | 3.3% | 7.6% | 1.9% |
| space1 | | | |
| Race | | | |
| | Rockford, IL | Grass Valley, CA | United States |
| White | 52.5% | 78.6% | 59.4% |
| Black | 21.0% | 0.5% | 12.2% |
| Asian | 3.5% | 1.7% | 5.6% |
| Native American | 0.0% | 0.0% | 0.6% |
| Hawaiian, Pacific Islander | 0.0% | 0.0% | 0.2% |
| Other | 0.2% | 0.2% | 0.4% |
| Two or More Races | 3.7% | 8.0% | 3.2% |
| Hispanic | 18.8% | 11.0% | 18.4% |
| space2 | | | |
| Marriage & Family | | | |
| | Rockford, IL | Grass Valley, CA | United States |
| Married Population | 41.9% | 35.2% | 49.8% |
| Currently Married | 39.8% | 32.9% | 48.0% |
| Married but Separated | 2.1% | 2.3% | 1.8% |
| Single Population | 58.1% | 64.8% | 50.2% |
| Never Married | 37.7% | 28.3% | 33.8% |
| Divorced | 13.8% | 22.3% | 10.8% |
| Widowed | 6.5% | 14.3% | 5.6% |
| space5 | | | |
| Household Size | 2.37 | 1.99 | 2.60 |
| Households | 61,304 | 6,495 | 124,010,992 |
| Family Households | 36,078 | 2,890 | 80,755,759 |
| Married couple, w/children | 22.5% | 24.8% | 30.5% |
| Married couple, no children | 38.4% | 33.7% | 42.9% |
| Non Family Households | 25,226 | 3,605 | 43,255,233 |
| Single householder, w/children | 26.5% | 24.9% | 15.8% |
| Single householder, no children | 12.7% | 16.6% | 10.8% |