| | Rockland, ME | Rock Island, IL | United States |
| Population | 6,977 | 37,519 | 329,725,481 |
| Female Population | 53.1% | 50.0% | 50.5% |
| Male Population | 46.9% | 50.0% | 49.5% |
| Median Age | 45.4 | 35.4 | 38.4 |
| space3 | | | |
| Population - 2010 | 7,295 | 38,973 | 309,327,143 |
| Population - 2000 | 7,609 | 39,684 | 285,036,114 |
| Population - 1990 | 7,972 | 40,552 | 251,960,433 |
| Pop. 2000 to Now | -5.6% | -7.1% | 15.6% |
| Pop. 1990 to Now | -9.9% | -9.1% | 30.8% |
| space4 | | | |
| Population Density | 543.3 | 2,226.0 | 93.4 |
| Land Area | 12.8 | 16.9 | 3,531,905.4 |
| Water Area | 2.2 | 0.2 | 264,836.8 |
| space | | | |
| Est. Total Population By Age | | | |
| | Rockland, ME | Rock Island, IL | United States |
| Age 0 to 4 | 3.8% | 6.2% | 5.9% |
| Age 5 to 9 | 5.3% | 5.3% | 6.1% |
| Age 10 to 14 | 6.4% | 6.9% | 6.6% |
| Age 15 to 17 | 3.5% | 3.9% | 3.9% |
| Age 18 to 20 | 2.7% | 8.5% | 4.0% |
| Age 21 to 24 | 4.4% | 5.9% | 5.2% |
| Age 25 to 34 | 13.6% | 12.8% | 13.8% |
| Age 35 to 44 | 9.7% | 11.4% | 12.9% |
| Age 45 to 54 | 8.3% | 9.9% | 12.6% |
| Age 55 to 59 | 9.1% | 5.7% | 6.7% |
| Age 60 to 64 | 11.2% | 6.3% | 6.3% |
| Age 65 to 74 | 12.2% | 10.0% | 9.6% |
| Age 75 to 84 | 7.1% | 4.5% | 4.5% |
| Age 85 and over | 2.8% | 2.5% | 1.9% |
| space1 | | | |
| Race | | | |
| | Rockland, ME | Rock Island, IL | United States |
| White | 95.4% | 61.1% | 59.4% |
| Black | 0.0% | 17.1% | 12.2% |
| Asian | 0.9% | 4.5% | 5.6% |
| Native American | 0.2% | 0.2% | 0.6% |
| Hawaiian, Pacific Islander | 0.0% | 0.1% | 0.2% |
| Other | 0.0% | 0.1% | 0.4% |
| Two or More Races | 2.6% | 3.2% | 3.2% |
| Hispanic | 0.9% | 13.7% | 18.4% |
| space2 | | | |
| Marriage & Family | | | |
| | Rockland, ME | Rock Island, IL | United States |
| Married Population | 38.6% | 39.4% | 49.8% |
| Currently Married | 37.2% | 37.6% | 48.0% |
| Married but Separated | 1.5% | 1.8% | 1.8% |
| Single Population | 61.4% | 60.6% | 50.2% |
| Never Married | 33.6% | 41.2% | 33.8% |
| Divorced | 20.6% | 12.6% | 10.8% |
| Widowed | 7.2% | 6.7% | 5.6% |
| space5 | | | |
| Household Size | 2.01 | 2.26 | 2.60 |
| Households | 3,367 | 15,285 | 124,010,992 |
| Family Households | 1,437 | 7,918 | 80,755,759 |
| Married couple, w/children | 21.5% | 27.4% | 30.5% |
| Married couple, no children | 53.0% | 39.9% | 42.9% |
| Non Family Households | 1,930 | 7,367 | 43,255,233 |
| Single householder, w/children | 21.2% | 21.8% | 15.8% |
| Single householder, no children | 4.4% | 10.8% | 10.8% |