| | St. Regis, MT | Lakeside, MT | United States |
| Population | 368 | 2,463 | 329,725,481 |
| Female Population | 53.3% | 58.8% | 50.5% |
| Male Population | 46.7% | 41.2% | 49.5% |
| Median Age | 29.4 | 47.8 | 38.4 |
| space3 | | | |
| Population - 2010 | 260 | 1,608 | 309,327,143 |
| Population - 2000 | 315 | 1,679 | 285,036,114 |
| Population - 1990 | 240 | 1,132 | 251,960,433 |
| Pop. 2000 to Now | 27.3% | 61.6% | 15.6% |
| Pop. 1990 to Now | 67.1% | 139.7% | 30.8% |
| space4 | | | |
| Population Density | 429.9 | 175.1 | 93.4 |
| Land Area | 0.9 | 14.1 | 3,531,905.4 |
| Water Area | 0.0 | 3.9 | 264,836.8 |
| space | | | |
| Est. Total Population By Age | | | |
| | St. Regis, MT | Lakeside, MT | United States |
| Age 0 to 4 | 13.3% | 7.5% | 5.9% |
| Age 5 to 9 | 16.3% | 8.3% | 6.1% |
| Age 10 to 14 | 6.0% | 4.2% | 6.6% |
| Age 15 to 17 | 7.3% | 4.7% | 3.9% |
| Age 18 to 20 | 0.3% | 2.1% | 4.0% |
| Age 21 to 24 | 3.8% | 2.2% | 5.2% |
| Age 25 to 34 | 16.0% | 10.2% | 13.8% |
| Age 35 to 44 | 9.2% | 7.1% | 12.9% |
| Age 45 to 54 | 3.8% | 7.7% | 12.6% |
| Age 55 to 59 | 4.1% | 3.3% | 6.7% |
| Age 60 to 64 | 2.7% | 14.3% | 6.3% |
| Age 65 to 74 | 14.4% | 20.1% | 9.6% |
| Age 75 to 84 | 2.7% | 4.3% | 4.5% |
| Age 85 and over | 0.0% | 4.1% | 1.9% |
| space1 | | | |
| Race | | | |
| | St. Regis, MT | Lakeside, MT | United States |
| White | 96.7% | 97.4% | 59.4% |
| Black | 0.3% | 0.0% | 12.2% |
| Asian | 0.0% | 0.1% | 5.6% |
| Native American | 0.0% | 0.0% | 0.6% |
| Hawaiian, Pacific Islander | 0.0% | 0.0% | 0.2% |
| Other | 0.0% | 0.0% | 0.4% |
| Two or More Races | 0.0% | 0.0% | 3.2% |
| Hispanic | 3.0% | 2.5% | 18.4% |
| space2 | | | |
| Marriage & Family | | | |
| | St. Regis, MT | Lakeside, MT | United States |
| Married Population | 46.8% | 57.9% | 49.8% |
| Currently Married | 38.8% | 56.4% | 48.0% |
| Married but Separated | 8.0% | 1.5% | 1.8% |
| Single Population | 53.2% | 42.1% | 50.2% |
| Never Married | 39.2% | 17.0% | 33.8% |
| Divorced | 8.9% | 11.5% | 10.8% |
| Widowed | 5.1% | 13.6% | 5.6% |
| space5 | | | |
| Household Size | 2.98 | 2.20 | 2.60 |
| Households | 120 | 1,104 | 124,010,992 |
| Family Households | 72 | 598 | 80,755,759 |
| Married couple, w/children | 26.4% | 40.8% | 30.5% |
| Married couple, no children | 23.6% | 51.8% | 42.9% |
| Non Family Households | 48 | 506 | 43,255,233 |
| Single householder, w/children | 36.1% | 5.0% | 15.8% |
| Single householder, no children | 13.9% | 2.3% | 10.8% |