| | Jefferson City, MT | Boulder, MT | United States |
| Population | 438 | 1,033 | 329,725,481 |
| Female Population | 47.5% | 49.1% | 50.5% |
| Male Population | 52.5% | 50.9% | 49.5% |
| Median Age | 47.9 | 40.2 | 38.4 |
| space3 | | | |
| Population - 2010 | 373 | 1,180 | 309,327,143 |
| Population - 2000 | 295 | 1,300 | 285,036,114 |
| Population - 1990 | 288 | 1,316 | 251,960,433 |
| Pop. 2000 to Now | 136.6% | -0.7% | 15.6% |
| Pop. 1990 to Now | 142.4% | -1.9% | 30.8% |
| space4 | | | |
| Population Density | 18.9 | 919.0 | 93.4 |
| Land Area | 23.2 | 1.1 | 3,531,905.4 |
| Water Area | 0.0 | 0.0 | 264,836.8 |
| space | | | |
| Est. Total Population By Age | | | |
| | Jefferson City, MT | Boulder, MT | United States |
| Age 0 to 4 | 5.0% | 9.8% | 5.9% |
| Age 5 to 9 | 14.6% | 10.0% | 6.1% |
| Age 10 to 14 | 5.0% | 2.7% | 6.6% |
| Age 15 to 17 | 0.0% | 1.6% | 3.9% |
| Age 18 to 20 | 0.0% | 3.6% | 4.0% |
| Age 21 to 24 | 0.0% | 8.2% | 5.2% |
| Age 25 to 34 | 16.9% | 10.1% | 13.8% |
| Age 35 to 44 | 0.0% | 15.5% | 12.9% |
| Age 45 to 54 | 15.5% | 10.8% | 12.6% |
| Age 55 to 59 | 3.9% | 6.8% | 6.7% |
| Age 60 to 64 | 7.1% | 7.2% | 6.3% |
| Age 65 to 74 | 27.4% | 7.4% | 9.6% |
| Age 75 to 84 | 4.6% | 4.6% | 4.5% |
| Age 85 and over | 0.0% | 1.8% | 1.9% |
| space1 | | | |
| Race | | | |
| | Jefferson City, MT | Boulder, MT | United States |
| White | 93.8% | 89.1% | 59.4% |
| Black | 0.0% | 0.0% | 12.2% |
| Asian | 0.0% | 0.0% | 5.6% |
| Native American | 0.0% | 5.3% | 0.6% |
| Hawaiian, Pacific Islander | 0.0% | 0.0% | 0.2% |
| Other | 0.0% | 0.0% | 0.4% |
| Two or More Races | 4.8% | 2.8% | 3.2% |
| Hispanic | 1.4% | 2.8% | 18.4% |
| space2 | | | |
| Marriage & Family | | | |
| | Jefferson City, MT | Boulder, MT | United States |
| Married Population | 57.6% | 40.3% | 49.8% |
| Currently Married | 57.6% | 36.6% | 48.0% |
| Married but Separated | 0.0% | 3.7% | 1.8% |
| Single Population | 42.4% | 59.7% | 50.2% |
| Never Married | 10.6% | 33.8% | 33.8% |
| Divorced | 24.2% | 21.6% | 10.8% |
| Widowed | 7.6% | 4.2% | 5.6% |
| space5 | | | |
| Household Size | 2.43 | 2.44 | 2.60 |
| Households | 180 | 378 | 124,010,992 |
| Family Households | 93 | 203 | 80,755,759 |
| Married couple, w/children | 30.1% | 34.0% | 30.5% |
| Married couple, no children | 64.5% | 36.9% | 42.9% |
| Non Family Households | 87 | 175 | 43,255,233 |
| Single householder, w/children | 0.0% | 21.7% | 15.8% |
| Single householder, no children | 5.4% | 7.4% | 10.8% |