| | St. Johnsville, NY | Amsterdam, NY | United States |
| Population | 2,582 | 18,218 | 329,725,481 |
| Female Population | 49.4% | 51.0% | 50.5% |
| Male Population | 50.6% | 49.1% | 49.5% |
| Median Age | 39.7 | 38.3 | 38.4 |
| space3 | | | |
| Population - 2010 | 2,642 | 18,613 | 309,327,143 |
| Population - 2000 | 2,565 | 18,355 | 285,036,114 |
| Population - 1990 | 2,773 | 20,714 | 251,960,433 |
| Pop. 2000 to Now | -2.0% | -3.5% | 15.6% |
| Pop. 1990 to Now | -9.3% | -14.5% | 30.8% |
| space4 | | | |
| Population Density | 153.3 | 3,102.5 | 93.4 |
| Land Area | 16.8 | 5.9 | 3,531,905.4 |
| Water Area | 0.5 | 0.4 | 264,836.8 |
| space | | | |
| Est. Total Population By Age | | | |
| | St. Johnsville, NY | Amsterdam, NY | United States |
| Age 0 to 4 | 8.1% | 5.8% | 5.9% |
| Age 5 to 9 | 5.2% | 7.0% | 6.1% |
| Age 10 to 14 | 6.8% | 6.3% | 6.6% |
| Age 15 to 17 | 3.6% | 5.4% | 3.9% |
| Age 18 to 20 | 2.7% | 3.6% | 4.0% |
| Age 21 to 24 | 5.2% | 4.5% | 5.2% |
| Age 25 to 34 | 8.4% | 13.5% | 13.8% |
| Age 35 to 44 | 15.0% | 11.4% | 12.9% |
| Age 45 to 54 | 9.1% | 12.2% | 12.6% |
| Age 55 to 59 | 3.4% | 6.2% | 6.7% |
| Age 60 to 64 | 9.6% | 6.6% | 6.3% |
| Age 65 to 74 | 12.9% | 10.9% | 9.6% |
| Age 75 to 84 | 4.8% | 4.4% | 4.5% |
| Age 85 and over | 5.3% | 2.3% | 1.9% |
| space1 | | | |
| Race | | | |
| | St. Johnsville, NY | Amsterdam, NY | United States |
| White | 92.1% | 60.4% | 59.4% |
| Black | 0.0% | 5.7% | 12.2% |
| Asian | 0.8% | 1.7% | 5.6% |
| Native American | 0.0% | 0.1% | 0.6% |
| Hawaiian, Pacific Islander | 0.0% | 0.0% | 0.2% |
| Other | 0.5% | 0.1% | 0.4% |
| Two or More Races | 1.7% | 1.4% | 3.2% |
| Hispanic | 4.8% | 30.6% | 18.4% |
| space2 | | | |
| Marriage & Family | | | |
| | St. Johnsville, NY | Amsterdam, NY | United States |
| Married Population | 44.4% | 37.5% | 49.8% |
| Currently Married | 41.4% | 35.0% | 48.0% |
| Married but Separated | 3.1% | 2.5% | 1.8% |
| Single Population | 55.6% | 62.5% | 50.2% |
| Never Married | 31.8% | 42.0% | 33.8% |
| Divorced | 15.4% | 13.7% | 10.8% |
| Widowed | 8.4% | 6.9% | 5.6% |
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| Household Size | 2.65 | 2.43 | 2.60 |
| Households | 935 | 7,383 | 124,010,992 |
| Family Households | 571 | 4,290 | 80,755,759 |
| Married couple, w/children | 22.4% | 18.8% | 30.5% |
| Married couple, no children | 46.8% | 37.9% | 42.9% |
| Non Family Households | 364 | 3,093 | 43,255,233 |
| Single householder, w/children | 19.3% | 30.7% | 15.8% |
| Single householder, no children | 11.6% | 12.7% | 10.8% |