| | Underhill, VT | Twisp, WA | United States |
| Population | 3,142 | 1,211 | 329,725,481 |
| Female Population | 52.2% | 53.8% | 50.5% |
| Male Population | 47.8% | 46.2% | 49.5% |
| Median Age | 45.7 | 44.3 | 38.4 |
| space3 | | | |
| Population - 2010 | 3,026 | 904 | 309,327,143 |
| Population - 2000 | 2,980 | 938 | 285,036,114 |
| Population - 1990 | 2,799 | 872 | 251,960,433 |
| Pop. 2000 to Now | 3.2% | 5.3% | 15.6% |
| Pop. 1990 to Now | 9.9% | 13.3% | 30.8% |
| space4 | | | |
| Population Density | 61.2 | 1,030.6 | 93.4 |
| Land Area | 51.3 | 1.2 | 3,531,905.4 |
| Water Area | 0.1 | 0.0 | 264,836.8 |
| space | | | |
| Est. Total Population By Age | | | |
| | Underhill, VT | Twisp, WA | United States |
| Age 0 to 4 | 4.5% | 2.7% | 5.9% |
| Age 5 to 9 | 9.8% | 3.8% | 6.1% |
| Age 10 to 14 | 4.4% | 10.7% | 6.6% |
| Age 15 to 17 | 5.6% | 2.6% | 3.9% |
| Age 18 to 20 | 1.1% | 1.6% | 4.0% |
| Age 21 to 24 | 3.3% | 5.2% | 5.2% |
| Age 25 to 34 | 12.2% | 9.9% | 13.8% |
| Age 35 to 44 | 7.9% | 14.2% | 12.9% |
| Age 45 to 54 | 14.6% | 13.3% | 12.6% |
| Age 55 to 59 | 7.7% | 6.6% | 6.7% |
| Age 60 to 64 | 8.6% | 8.2% | 6.3% |
| Age 65 to 74 | 14.5% | 13.6% | 9.6% |
| Age 75 to 84 | 5.2% | 6.4% | 4.5% |
| Age 85 and over | 0.7% | 1.2% | 1.9% |
| space1 | | | |
| Race | | | |
| | Underhill, VT | Twisp, WA | United States |
| White | 95.7% | 77.0% | 59.4% |
| Black | 0.4% | 0.0% | 12.2% |
| Asian | 0.8% | 2.3% | 5.6% |
| Native American | 0.0% | 0.7% | 0.6% |
| Hawaiian, Pacific Islander | 0.0% | 0.0% | 0.2% |
| Other | 0.0% | 0.0% | 0.4% |
| Two or More Races | 0.9% | 0.2% | 3.2% |
| Hispanic | 2.1% | 19.7% | 18.4% |
| space2 | | | |
| Marriage & Family | | | |
| | Underhill, VT | Twisp, WA | United States |
| Married Population | 68.6% | 49.8% | 49.8% |
| Currently Married | 68.4% | 48.6% | 48.0% |
| Married but Separated | 0.2% | 1.2% | 1.8% |
| Single Population | 31.4% | 50.2% | 50.2% |
| Never Married | 22.0% | 24.7% | 33.8% |
| Divorced | 6.6% | 24.4% | 10.8% |
| Widowed | 2.8% | 1.1% | 5.6% |
| space5 | | | |
| Household Size | 2.45 | 2.19 | 2.60 |
| Households | 1,285 | 554 | 124,010,992 |
| Family Households | 909 | 341 | 80,755,759 |
| Married couple, w/children | 39.7% | 32.0% | 30.5% |
| Married couple, no children | 52.3% | 44.6% | 42.9% |
| Non Family Households | 376 | 213 | 43,255,233 |
| Single householder, w/children | 6.6% | 18.2% | 15.8% |
| Single householder, no children | 1.4% | 5.3% | 10.8% |