| | Rockford, IL | Erie, CO | United States |
| Population | 148,942 | 29,367 | 329,725,481 |
| Female Population | 51.1% | 49.9% | 50.5% |
| Male Population | 48.9% | 50.1% | 49.5% |
| Median Age | 37.6 | 37.1 | 38.4 |
| space3 | | | |
| Population - 2010 | 153,173 | 18,395 | 309,327,143 |
| Population - 2000 | 150,115 | 6,291 | 285,036,114 |
| Population - 1990 | 139,426 | 1,258 | 251,960,433 |
| Pop. 2000 to Now | -3.5% | 381.9% | 15.6% |
| Pop. 1990 to Now | 3.9% | 2,310.0% | 30.8% |
| space4 | | | |
| Population Density | 2,313.9 | 1,495.1 | 93.4 |
| Land Area | 64.4 | 19.6 | 3,531,905.4 |
| Water Area | 1.0 | 0.1 | 264,836.8 |
| space | | | |
| Est. Total Population By Age | | | |
| | Rockford, IL | Erie, CO | United States |
| Age 0 to 4 | 6.8% | 7.8% | 5.9% |
| Age 5 to 9 | 6.8% | 9.0% | 6.1% |
| Age 10 to 14 | 7.3% | 9.5% | 6.6% |
| Age 15 to 17 | 4.1% | 4.8% | 3.9% |
| Age 18 to 20 | 3.2% | 1.8% | 4.0% |
| Age 21 to 24 | 5.3% | 3.1% | 5.2% |
| Age 25 to 34 | 13.3% | 11.0% | 13.8% |
| Age 35 to 44 | 11.9% | 17.7% | 12.9% |
| Age 45 to 54 | 11.7% | 14.8% | 12.6% |
| Age 55 to 59 | 6.6% | 6.1% | 6.7% |
| Age 60 to 64 | 6.2% | 4.9% | 6.3% |
| Age 65 to 74 | 9.5% | 6.1% | 9.6% |
| Age 75 to 84 | 4.1% | 2.9% | 4.5% |
| Age 85 and over | 3.3% | 0.6% | 1.9% |
| space1 | | | |
| Race | | | |
| | Rockford, IL | Erie, CO | United States |
| White | 52.5% | 81.9% | 59.4% |
| Black | 21.0% | 0.0% | 12.2% |
| Asian | 3.5% | 5.4% | 5.6% |
| Native American | 0.0% | 0.1% | 0.6% |
| Hawaiian, Pacific Islander | 0.0% | 0.1% | 0.2% |
| Other | 0.2% | 0.1% | 0.4% |
| Two or More Races | 3.7% | 3.2% | 3.2% |
| Hispanic | 18.8% | 9.3% | 18.4% |
| space2 | | | |
| Marriage & Family | | | |
| | Rockford, IL | Erie, CO | United States |
| Married Population | 41.9% | 66.3% | 49.8% |
| Currently Married | 39.8% | 65.9% | 48.0% |
| Married but Separated | 2.1% | 0.3% | 1.8% |
| Single Population | 58.1% | 33.7% | 50.2% |
| Never Married | 37.7% | 22.8% | 33.8% |
| Divorced | 13.8% | 7.8% | 10.8% |
| Widowed | 6.5% | 3.1% | 5.6% |
| space5 | | | |
| Household Size | 2.37 | 2.97 | 2.60 |
| Households | 61,304 | 9,879 | 124,010,992 |
| Family Households | 36,078 | 7,969 | 80,755,759 |
| Married couple, w/children | 22.5% | 49.7% | 30.5% |
| Married couple, no children | 38.4% | 36.8% | 42.9% |
| Non Family Households | 25,226 | 1,910 | 43,255,233 |
| Single householder, w/children | 26.5% | 9.5% | 15.8% |
| Single householder, no children | 12.7% | 4.1% | 10.8% |