| | Ennis, MT | Idaho Falls, ID | United States |
| Population | 673 | 64,399 | 329,725,481 |
| Female Population | 45.6% | 50.5% | 50.5% |
| Male Population | 54.4% | 49.6% | 49.5% |
| Median Age | 58.2 | 33.6 | 38.4 |
| space3 | | | |
| Population - 2010 | 839 | 57,998 | 309,327,143 |
| Population - 2000 | 840 | 50,730 | 285,036,114 |
| Population - 1990 | 773 | 43,929 | 251,960,433 |
| Pop. 2000 to Now | 24.1% | 26.4% | 15.6% |
| Pop. 1990 to Now | 34.8% | 46.0% | 30.8% |
| space4 | | | |
| Population Density | 911.9 | 2,758.2 | 93.4 |
| Land Area | 0.7 | 23.3 | 3,531,905.4 |
| Water Area | 0.0 | 0.5 | 264,836.8 |
| space | | | |
| Est. Total Population By Age | | | |
| | Ennis, MT | Idaho Falls, ID | United States |
| Age 0 to 4 | 0.0% | 7.3% | 5.9% |
| Age 5 to 9 | 6.4% | 8.3% | 6.1% |
| Age 10 to 14 | 0.0% | 8.1% | 6.6% |
| Age 15 to 17 | 0.6% | 4.7% | 3.9% |
| Age 18 to 20 | 0.0% | 4.0% | 4.0% |
| Age 21 to 24 | 0.0% | 5.0% | 5.2% |
| Age 25 to 34 | 11.6% | 14.6% | 13.8% |
| Age 35 to 44 | 14.9% | 13.2% | 12.9% |
| Age 45 to 54 | 15.9% | 10.3% | 12.6% |
| Age 55 to 59 | 5.6% | 5.8% | 6.7% |
| Age 60 to 64 | 11.3% | 5.3% | 6.3% |
| Age 65 to 74 | 20.5% | 7.5% | 9.6% |
| Age 75 to 84 | 6.8% | 4.4% | 4.5% |
| Age 85 and over | 6.4% | 1.6% | 1.9% |
| space1 | | | |
| Race | | | |
| | Ennis, MT | Idaho Falls, ID | United States |
| White | 94.1% | 77.0% | 59.4% |
| Black | 0.3% | 0.4% | 12.2% |
| Asian | 0.0% | 0.9% | 5.6% |
| Native American | 0.0% | 0.6% | 0.6% |
| Hawaiian, Pacific Islander | 0.0% | 0.2% | 0.2% |
| Other | 2.1% | 0.2% | 0.4% |
| Two or More Races | 0.0% | 3.1% | 3.2% |
| Hispanic | 3.6% | 17.5% | 18.4% |
| space2 | | | |
| Marriage & Family | | | |
| | Ennis, MT | Idaho Falls, ID | United States |
| Married Population | 50.6% | 52.0% | 49.8% |
| Currently Married | 46.8% | 50.3% | 48.0% |
| Married but Separated | 3.8% | 1.7% | 1.8% |
| Single Population | 49.4% | 48.0% | 50.2% |
| Never Married | 25.6% | 29.0% | 33.8% |
| Divorced | 15.4% | 14.1% | 10.8% |
| Widowed | 8.4% | 4.9% | 5.6% |
| space5 | | | |
| Household Size | 1.74 | 2.66 | 2.60 |
| Households | 366 | 23,875 | 124,010,992 |
| Family Households | 132 | 15,317 | 80,755,759 |
| Married couple, w/children | 18.9% | 35.3% | 30.5% |
| Married couple, no children | 81.1% | 38.5% | 42.9% |
| Non Family Households | 234 | 8,558 | 43,255,233 |
| Single householder, w/children | 0.0% | 19.4% | 15.8% |
| Single householder, no children | 0.0% | 6.7% | 10.8% |