| | Alder, MT | Ennis, MT | United States |
| Population | 135 | 673 | 329,725,481 |
| Female Population | 38.5% | 45.6% | 50.5% |
| Male Population | 61.5% | 54.4% | 49.5% |
| Median Age | 58.1 | 58.2 | 38.4 |
| space3 | | | |
| Population - 2010 | 147 | 839 | 309,327,143 |
| Population - 2000 | 116 | 840 | 285,036,114 |
| Population - 1990 | 85 | 773 | 251,960,433 |
| Pop. 2000 to Now | -15.5% | 24.1% | 15.6% |
| Pop. 1990 to Now | 15.3% | 34.8% | 30.8% |
| space4 | | | |
| Population Density | 67.3 | 911.9 | 93.4 |
| Land Area | 2.0 | 0.7 | 3,531,905.4 |
| Water Area | 0.0 | 0.0 | 264,836.8 |
| space | | | |
| Est. Total Population By Age | | | |
| | Alder, MT | Ennis, MT | United States |
| Age 0 to 4 | 5.2% | 0.0% | 5.9% |
| Age 5 to 9 | 3.0% | 6.4% | 6.1% |
| Age 10 to 14 | 5.9% | 0.0% | 6.6% |
| Age 15 to 17 | 0.0% | 0.6% | 3.9% |
| Age 18 to 20 | 0.0% | 0.0% | 4.0% |
| Age 21 to 24 | 0.0% | 0.0% | 5.2% |
| Age 25 to 34 | 5.9% | 11.6% | 13.8% |
| Age 35 to 44 | 13.3% | 14.9% | 12.9% |
| Age 45 to 54 | 8.9% | 15.9% | 12.6% |
| Age 55 to 59 | 20.7% | 5.6% | 6.7% |
| Age 60 to 64 | 1.5% | 11.3% | 6.3% |
| Age 65 to 74 | 18.5% | 20.5% | 9.6% |
| Age 75 to 84 | 8.9% | 6.8% | 4.5% |
| Age 85 and over | 8.1% | 6.4% | 1.9% |
| space1 | | | |
| Race | | | |
| | Alder, MT | Ennis, MT | United States |
| White | 100.0% | 94.1% | 59.4% |
| Black | 0.0% | 0.3% | 12.2% |
| Asian | 0.0% | 0.0% | 5.6% |
| Native American | 0.0% | 0.0% | 0.6% |
| Hawaiian, Pacific Islander | 0.0% | 0.0% | 0.2% |
| Other | 0.0% | 2.1% | 0.4% |
| Two or More Races | 0.0% | 0.0% | 3.2% |
| Hispanic | 0.0% | 3.6% | 18.4% |
| space2 | | | |
| Marriage & Family | | | |
| | Alder, MT | Ennis, MT | United States |
| Married Population | 66.4% | 50.6% | 49.8% |
| Currently Married | 66.4% | 46.8% | 48.0% |
| Married but Separated | 0.0% | 3.8% | 1.8% |
| Single Population | 33.6% | 49.4% | 50.2% |
| Never Married | 16.4% | 25.6% | 33.8% |
| Divorced | 15.5% | 15.4% | 10.8% |
| Widowed | 1.7% | 8.4% | 5.6% |
| space5 | | | |
| Household Size | 2.50 | 1.74 | 2.60 |
| Households | 54 | 366 | 124,010,992 |
| Family Households | 33 | 132 | 80,755,759 |
| Married couple, w/children | 30.3% | 18.9% | 30.5% |
| Married couple, no children | 57.6% | 81.1% | 42.9% |
| Non Family Households | 21 | 234 | 43,255,233 |
| Single householder, w/children | 0.0% | 0.0% | 15.8% |
| Single householder, no children | 12.1% | 0.0% | 10.8% |