| | Rock Island, IL | Amarillo, TX | United States |
| Population | 37,519 | 200,371 | 329,725,481 |
| Female Population | 50.0% | 50.8% | 50.5% |
| Male Population | 50.0% | 49.2% | 49.5% |
| Median Age | 35.4 | 34.1 | 38.4 |
| space3 | | | |
| Population - 2010 | 38,973 | 191,260 | 309,327,143 |
| Population - 2000 | 39,684 | 173,627 | 285,036,114 |
| Population - 1990 | 40,552 | 157,615 | 251,960,433 |
| Pop. 2000 to Now | -7.1% | 15.0% | 15.6% |
| Pop. 1990 to Now | -9.1% | 26.7% | 30.8% |
| space4 | | | |
| Population Density | 2,226.0 | 1,972.0 | 93.4 |
| Land Area | 16.9 | 101.6 | 3,531,905.4 |
| Water Area | 0.2 | 1.6 | 264,836.8 |
| space | | | |
| Est. Total Population By Age | | | |
| | Rock Island, IL | Amarillo, TX | United States |
| Age 0 to 4 | 6.2% | 7.4% | 5.9% |
| Age 5 to 9 | 5.3% | 7.8% | 6.1% |
| Age 10 to 14 | 6.9% | 7.5% | 6.6% |
| Age 15 to 17 | 3.9% | 4.4% | 3.9% |
| Age 18 to 20 | 8.5% | 3.8% | 4.0% |
| Age 21 to 24 | 5.9% | 5.2% | 5.2% |
| Age 25 to 34 | 12.8% | 15.1% | 13.8% |
| Age 35 to 44 | 11.4% | 13.5% | 12.9% |
| Age 45 to 54 | 9.9% | 10.8% | 12.6% |
| Age 55 to 59 | 5.7% | 5.2% | 6.7% |
| Age 60 to 64 | 6.3% | 5.5% | 6.3% |
| Age 65 to 74 | 10.0% | 8.2% | 9.6% |
| Age 75 to 84 | 4.5% | 3.9% | 4.5% |
| Age 85 and over | 2.5% | 1.7% | 1.9% |
| space1 | | | |
| Race | | | |
| | Rock Island, IL | Amarillo, TX | United States |
| White | 61.1% | 52.5% | 59.4% |
| Black | 17.1% | 6.7% | 12.2% |
| Asian | 4.5% | 4.1% | 5.6% |
| Native American | 0.2% | 0.3% | 0.6% |
| Hawaiian, Pacific Islander | 0.1% | 0.1% | 0.2% |
| Other | 0.1% | 0.1% | 0.4% |
| Two or More Races | 3.2% | 2.2% | 3.2% |
| Hispanic | 13.7% | 34.0% | 18.4% |
| space2 | | | |
| Marriage & Family | | | |
| | Rock Island, IL | Amarillo, TX | United States |
| Married Population | 39.4% | 52.4% | 49.8% |
| Currently Married | 37.6% | 50.0% | 48.0% |
| Married but Separated | 1.8% | 2.4% | 1.8% |
| Single Population | 60.6% | 47.6% | 50.2% |
| Never Married | 41.2% | 29.6% | 33.8% |
| Divorced | 12.6% | 12.0% | 10.8% |
| Widowed | 6.7% | 6.0% | 5.6% |
| space5 | | | |
| Household Size | 2.26 | 2.53 | 2.60 |
| Households | 15,285 | 78,540 | 124,010,992 |
| Family Households | 7,918 | 50,436 | 80,755,759 |
| Married couple, w/children | 27.4% | 32.5% | 30.5% |
| Married couple, no children | 39.9% | 37.9% | 42.9% |
| Non Family Households | 7,367 | 28,104 | 43,255,233 |
| Single householder, w/children | 21.8% | 20.7% | 15.8% |
| Single householder, no children | 10.8% | 8.9% | 10.8% |