| | Johnstown, NY | Rochelle, IL | United States |
| Population | 8,247 | 9,380 | 329,725,481 |
| Female Population | 51.2% | 51.9% | 50.5% |
| Male Population | 48.8% | 48.1% | 49.5% |
| Median Age | 44.4 | 40 | 38.4 |
| space3 | | | |
| Population - 2010 | 8,670 | 9,555 | 309,327,143 |
| Population - 2000 | 8,511 | 9,424 | 285,036,114 |
| Population - 1990 | 9,058 | 8,769 | 251,960,433 |
| Pop. 2000 to Now | -4.8% | -4.8% | 15.6% |
| Pop. 1990 to Now | -10.6% | 2.4% | 30.8% |
| space4 | | | |
| Population Density | 1,711.0 | 712.6 | 93.4 |
| Land Area | 4.8 | 13.2 | 3,531,905.4 |
| Water Area | 0.0 | 0.0 | 264,836.8 |
| space | | | |
| Est. Total Population By Age | | | |
| | Johnstown, NY | Rochelle, IL | United States |
| Age 0 to 4 | 4.5% | 2.7% | 5.9% |
| Age 5 to 9 | 5.3% | 5.0% | 6.1% |
| Age 10 to 14 | 4.7% | 5.3% | 6.6% |
| Age 15 to 17 | 3.9% | 5.8% | 3.9% |
| Age 18 to 20 | 1.9% | 6.7% | 4.0% |
| Age 21 to 24 | 3.5% | 6.6% | 5.2% |
| Age 25 to 34 | 13.0% | 12.6% | 13.8% |
| Age 35 to 44 | 14.8% | 11.3% | 12.9% |
| Age 45 to 54 | 17.5% | 12.8% | 12.6% |
| Age 55 to 59 | 5.7% | 6.5% | 6.7% |
| Age 60 to 64 | 6.6% | 6.5% | 6.3% |
| Age 65 to 74 | 11.9% | 7.9% | 9.6% |
| Age 75 to 84 | 3.4% | 6.3% | 4.5% |
| Age 85 and over | 3.3% | 3.9% | 1.9% |
| space1 | | | |
| Race | | | |
| | Johnstown, NY | Rochelle, IL | United States |
| White | 92.9% | 72.0% | 59.4% |
| Black | 1.0% | 2.5% | 12.2% |
| Asian | 0.2% | 0.3% | 5.6% |
| Native American | 0.0% | 0.6% | 0.6% |
| Hawaiian, Pacific Islander | 0.0% | 0.0% | 0.2% |
| Other | 0.0% | 0.0% | 0.4% |
| Two or More Races | 2.7% | 2.3% | 3.2% |
| Hispanic | 3.2% | 22.4% | 18.4% |
| space2 | | | |
| Marriage & Family | | | |
| | Johnstown, NY | Rochelle, IL | United States |
| Married Population | 45.7% | 35.3% | 49.8% |
| Currently Married | 43.1% | 33.9% | 48.0% |
| Married but Separated | 2.6% | 1.3% | 1.8% |
| Single Population | 54.3% | 64.7% | 50.2% |
| Never Married | 32.1% | 36.4% | 33.8% |
| Divorced | 14.2% | 18.5% | 10.8% |
| Widowed | 8.0% | 9.8% | 5.6% |
| space5 | | | |
| Household Size | 2.18 | 2.25 | 2.60 |
| Households | 3,717 | 4,130 | 124,010,992 |
| Family Households | 2,097 | 2,194 | 80,755,759 |
| Married couple, w/children | 25.7% | 21.5% | 30.5% |
| Married couple, no children | 45.5% | 37.0% | 42.9% |
| Non Family Households | 1,620 | 1,936 | 43,255,233 |
| Single householder, w/children | 22.5% | 25.3% | 15.8% |
| Single householder, no children | 6.3% | 16.2% | 10.8% |