| | Rockwell City, IA | Hilo, HI | United States |
| Population | 2,362 | 46,559 | 329,725,481 |
| Female Population | 41.1% | 51.3% | 50.5% |
| Male Population | 58.9% | 48.7% | 49.5% |
| Median Age | 38.4 | 39.9 | 38.4 |
| space3 | | | |
| Population - 2010 | 2,215 | 48,795 | 309,327,143 |
| Population - 2000 | 2,264 | 40,759 | 285,036,114 |
| Population - 1990 | 1,981 | 37,808 | 251,960,433 |
| Pop. 2000 to Now | -9.9% | 16.3% | 15.6% |
| Pop. 1990 to Now | 3.0% | 25.3% | 30.8% |
| space4 | | | |
| Population Density | 559.1 | 872.1 | 93.4 |
| Land Area | 4.2 | 53.4 | 3,531,905.4 |
| Water Area | 0.0 | 4.9 | 264,836.8 |
| space | | | |
| Est. Total Population By Age | | | |
| | Rockwell City, IA | Hilo, HI | United States |
| Age 0 to 4 | 3.3% | 4.3% | 5.9% |
| Age 5 to 9 | 5.3% | 6.5% | 6.1% |
| Age 10 to 14 | 6.1% | 7.2% | 6.6% |
| Age 15 to 17 | 4.9% | 3.9% | 3.9% |
| Age 18 to 20 | 3.9% | 4.1% | 4.0% |
| Age 21 to 24 | 4.7% | 4.9% | 5.2% |
| Age 25 to 34 | 15.9% | 13.1% | 13.8% |
| Age 35 to 44 | 17.1% | 11.9% | 12.9% |
| Age 45 to 54 | 9.3% | 10.2% | 12.6% |
| Age 55 to 59 | 6.2% | 5.5% | 6.7% |
| Age 60 to 64 | 5.1% | 7.7% | 6.3% |
| Age 65 to 74 | 8.3% | 11.3% | 9.6% |
| Age 75 to 84 | 6.1% | 5.9% | 4.5% |
| Age 85 and over | 3.9% | 3.6% | 1.9% |
| space1 | | | |
| Race | | | |
| | Rockwell City, IA | Hilo, HI | United States |
| White | 91.6% | 15.7% | 59.4% |
| Black | 3.3% | 0.7% | 12.2% |
| Asian | 0.7% | 31.1% | 5.6% |
| Native American | 0.0% | 0.0% | 0.6% |
| Hawaiian, Pacific Islander | 0.0% | 10.5% | 0.2% |
| Other | 0.1% | 0.0% | 0.4% |
| Two or More Races | 2.0% | 29.2% | 3.2% |
| Hispanic | 2.3% | 12.8% | 18.4% |
| space2 | | | |
| Marriage & Family | | | |
| | Rockwell City, IA | Hilo, HI | United States |
| Married Population | 41.2% | 45.2% | 49.8% |
| Currently Married | 37.1% | 43.6% | 48.0% |
| Married but Separated | 4.1% | 1.5% | 1.8% |
| Single Population | 58.8% | 54.8% | 50.2% |
| Never Married | 34.4% | 38.0% | 33.8% |
| Divorced | 16.7% | 10.1% | 10.8% |
| Widowed | 7.6% | 6.7% | 5.6% |
| space5 | | | |
| Household Size | 2.30 | 2.80 | 2.60 |
| Households | 770 | 16,189 | 124,010,992 |
| Family Households | 472 | 10,681 | 80,755,759 |
| Married couple, w/children | 26.1% | 24.5% | 30.5% |
| Married couple, no children | 46.8% | 42.6% | 42.9% |
| Non Family Households | 298 | 5,508 | 43,255,233 |
| Single householder, w/children | 21.6% | 18.7% | 15.8% |
| Single householder, no children | 5.5% | 14.1% | 10.8% |