| | Sidney, MT | Miles City, MT | United States |
| Population | 6,240 | 8,441 | 329,725,481 |
| Female Population | 51.4% | 50.4% | 50.5% |
| Male Population | 48.6% | 49.6% | 49.5% |
| Median Age | 38.4 | 41.9 | 38.4 |
| space3 | | | |
| Population - 2010 | 5,331 | 8,395 | 309,327,143 |
| Population - 2000 | 4,774 | 8,487 | 285,036,114 |
| Population - 1990 | 5,217 | 8,461 | 251,960,433 |
| Pop. 2000 to Now | 31.9% | -3.6% | 15.6% |
| Pop. 1990 to Now | 20.7% | -3.3% | 30.8% |
| space4 | | | |
| Population Density | 1,897.2 | 2,510.7 | 93.4 |
| Land Area | 3.3 | 3.4 | 3,531,905.4 |
| Water Area | 0.0 | 0.0 | 264,836.8 |
| space | | | |
| Est. Total Population By Age | | | |
| | Sidney, MT | Miles City, MT | United States |
| Age 0 to 4 | 6.0% | 4.9% | 5.9% |
| Age 5 to 9 | 6.0% | 5.4% | 6.1% |
| Age 10 to 14 | 8.6% | 5.7% | 6.6% |
| Age 15 to 17 | 4.4% | 3.4% | 3.9% |
| Age 18 to 20 | 5.3% | 4.9% | 4.0% |
| Age 21 to 24 | 2.9% | 4.3% | 5.2% |
| Age 25 to 34 | 14.1% | 13.2% | 13.8% |
| Age 35 to 44 | 13.8% | 11.9% | 12.9% |
| Age 45 to 54 | 12.2% | 11.7% | 12.6% |
| Age 55 to 59 | 5.8% | 7.7% | 6.7% |
| Age 60 to 64 | 7.3% | 7.4% | 6.3% |
| Age 65 to 74 | 9.5% | 10.4% | 9.6% |
| Age 75 to 84 | 2.6% | 6.7% | 4.5% |
| Age 85 and over | 1.5% | 2.5% | 1.9% |
| space1 | | | |
| Race | | | |
| | Sidney, MT | Miles City, MT | United States |
| White | 84.0% | 90.3% | 59.4% |
| Black | 0.0% | 1.1% | 12.2% |
| Asian | 0.0% | 0.3% | 5.6% |
| Native American | 0.2% | 0.8% | 0.6% |
| Hawaiian, Pacific Islander | 1.9% | 0.5% | 0.2% |
| Other | 0.0% | 0.0% | 0.4% |
| Two or More Races | 7.0% | 2.7% | 3.2% |
| Hispanic | 6.9% | 4.3% | 18.4% |
| space2 | | | |
| Marriage & Family | | | |
| | Sidney, MT | Miles City, MT | United States |
| Married Population | 49.9% | 47.5% | 49.8% |
| Currently Married | 48.3% | 44.6% | 48.0% |
| Married but Separated | 1.7% | 2.9% | 1.8% |
| Single Population | 50.1% | 52.5% | 50.2% |
| Never Married | 28.7% | 30.1% | 33.8% |
| Divorced | 13.1% | 13.9% | 10.8% |
| Widowed | 8.3% | 8.5% | 5.6% |
| space5 | | | |
| Household Size | 2.48 | 2.31 | 2.60 |
| Households | 2,502 | 3,510 | 124,010,992 |
| Family Households | 1,469 | 1,981 | 80,755,759 |
| Married couple, w/children | 28.2% | 33.6% | 30.5% |
| Married couple, no children | 48.0% | 42.6% | 42.9% |
| Non Family Households | 1,033 | 1,529 | 43,255,233 |
| Single householder, w/children | 15.4% | 13.4% | 15.8% |
| Single householder, no children | 8.4% | 10.5% | 10.8% |