| | Johnstown, PA | Nashua, NH | United States |
| Population | 18,647 | 90,659 | 329,725,481 |
| Female Population | 53.0% | 49.4% | 50.5% |
| Male Population | 47.0% | 50.6% | 49.5% |
| Median Age | 44.4 | 39.6 | 38.4 |
| space3 | | | |
| Population - 2010 | 20,944 | 86,569 | 309,327,143 |
| Population - 2000 | 23,906 | 86,605 | 285,036,114 |
| Population - 1990 | 28,134 | 79,662 | 251,960,433 |
| Pop. 2000 to Now | -20.8% | 3.0% | 15.6% |
| Pop. 1990 to Now | -32.7% | 11.9% | 30.8% |
| space4 | | | |
| Population Density | 3,164.3 | 2,940.3 | 93.4 |
| Land Area | 5.9 | 30.8 | 3,531,905.4 |
| Water Area | 0.2 | 0.9 | 264,836.8 |
| space | | | |
| Est. Total Population By Age | | | |
| | Johnstown, PA | Nashua, NH | United States |
| Age 0 to 4 | 6.2% | 5.5% | 5.9% |
| Age 5 to 9 | 7.3% | 5.2% | 6.1% |
| Age 10 to 14 | 6.4% | 5.7% | 6.6% |
| Age 15 to 17 | 3.4% | 3.2% | 3.9% |
| Age 18 to 20 | 2.9% | 2.8% | 4.0% |
| Age 21 to 24 | 3.1% | 5.8% | 5.2% |
| Age 25 to 34 | 11.3% | 16.2% | 13.8% |
| Age 35 to 44 | 9.9% | 12.0% | 12.9% |
| Age 45 to 54 | 13.4% | 13.4% | 12.6% |
| Age 55 to 59 | 7.0% | 6.8% | 6.7% |
| Age 60 to 64 | 9.0% | 7.3% | 6.3% |
| Age 65 to 74 | 11.7% | 9.7% | 9.6% |
| Age 75 to 84 | 5.4% | 4.4% | 4.5% |
| Age 85 and over | 2.9% | 2.1% | 1.9% |
| space1 | | | |
| Race | | | |
| | Johnstown, PA | Nashua, NH | United States |
| White | 72.1% | 73.2% | 59.4% |
| Black | 16.2% | 2.2% | 12.2% |
| Asian | 0.4% | 8.0% | 5.6% |
| Native American | 0.0% | 0.1% | 0.6% |
| Hawaiian, Pacific Islander | 0.0% | 0.0% | 0.2% |
| Other | 1.1% | 0.2% | 0.4% |
| Two or More Races | 5.6% | 3.1% | 3.2% |
| Hispanic | 4.6% | 13.2% | 18.4% |
| space2 | | | |
| Marriage & Family | | | |
| | Johnstown, PA | Nashua, NH | United States |
| Married Population | 35.5% | 47.3% | 49.8% |
| Currently Married | 31.5% | 45.5% | 48.0% |
| Married but Separated | 4.0% | 1.8% | 1.8% |
| Single Population | 64.5% | 52.7% | 50.2% |
| Never Married | 40.8% | 33.7% | 33.8% |
| Divorced | 15.3% | 13.0% | 10.8% |
| Widowed | 8.4% | 6.0% | 5.6% |
| space5 | | | |
| Household Size | 2.06 | 2.40 | 2.60 |
| Households | 8,991 | 37,119 | 124,010,992 |
| Family Households | 4,208 | 21,905 | 80,755,759 |
| Married couple, w/children | 12.6% | 29.6% | 30.5% |
| Married couple, no children | 36.8% | 43.6% | 42.9% |
| Non Family Households | 4,783 | 15,214 | 43,255,233 |
| Single householder, w/children | 32.5% | 14.5% | 15.8% |
| Single householder, no children | 18.0% | 12.3% | 10.8% |