| | Hermosa, SD | Billings, MT | United States |
| Population | 397 | 115,689 | 329,725,481 |
| Female Population | 49.6% | 50.4% | 50.5% |
| Male Population | 50.4% | 49.6% | 49.5% |
| Median Age | 45.1 | 37.6 | 38.4 |
| space3 | | | |
| Population - 2010 | 398 | 104,524 | 309,327,143 |
| Population - 2000 | 315 | 89,847 | 285,036,114 |
| Population - 1990 | 242 | 81,151 | 251,960,433 |
| Pop. 2000 to Now | 29.8% | 22.1% | 15.6% |
| Pop. 1990 to Now | 69.0% | 35.2% | 30.8% |
| space4 | | | |
| Population Density | 825.4 | 2,630.3 | 93.4 |
| Land Area | 0.5 | 44.0 | 3,531,905.4 |
| Water Area | 0.0 | 0.1 | 264,836.8 |
| space | | | |
| Est. Total Population By Age | | | |
| | Hermosa, SD | Billings, MT | United States |
| Age 0 to 4 | 0.3% | 6.2% | 5.9% |
| Age 5 to 9 | 13.6% | 6.3% | 6.1% |
| Age 10 to 14 | 9.6% | 6.7% | 6.6% |
| Age 15 to 17 | 2.8% | 3.8% | 3.9% |
| Age 18 to 20 | 2.0% | 3.3% | 4.0% |
| Age 21 to 24 | 2.5% | 5.4% | 5.2% |
| Age 25 to 34 | 6.3% | 14.7% | 13.8% |
| Age 35 to 44 | 12.3% | 13.2% | 12.9% |
| Age 45 to 54 | 16.9% | 10.6% | 12.6% |
| Age 55 to 59 | 11.1% | 5.7% | 6.7% |
| Age 60 to 64 | 2.8% | 6.7% | 6.3% |
| Age 65 to 74 | 14.4% | 10.0% | 9.6% |
| Age 75 to 84 | 4.5% | 5.0% | 4.5% |
| Age 85 and over | 1.0% | 2.4% | 1.9% |
| space1 | | | |
| Race | | | |
| | Hermosa, SD | Billings, MT | United States |
| White | 65.7% | 83.7% | 59.4% |
| Black | 0.0% | 0.5% | 12.2% |
| Asian | 1.0% | 0.8% | 5.6% |
| Native American | 6.3% | 4.2% | 0.6% |
| Hawaiian, Pacific Islander | 0.0% | 0.0% | 0.2% |
| Other | 0.0% | 0.2% | 0.4% |
| Two or More Races | 5.3% | 3.6% | 3.2% |
| Hispanic | 21.7% | 6.9% | 18.4% |
| space2 | | | |
| Marriage & Family | | | |
| | Hermosa, SD | Billings, MT | United States |
| Married Population | 51.6% | 48.3% | 49.8% |
| Currently Married | 50.3% | 47.5% | 48.0% |
| Married but Separated | 1.3% | 0.8% | 1.8% |
| Single Population | 48.4% | 51.7% | 50.2% |
| Never Married | 33.2% | 31.3% | 33.8% |
| Divorced | 12.5% | 14.7% | 10.8% |
| Widowed | 2.6% | 5.6% | 5.6% |
| space5 | | | |
| Household Size | 2.63 | 2.33 | 2.60 |
| Households | 151 | 48,478 | 124,010,992 |
| Family Households | 115 | 28,249 | 80,755,759 |
| Married couple, w/children | 13.9% | 31.5% | 30.5% |
| Married couple, no children | 56.5% | 43.8% | 42.9% |
| Non Family Households | 36 | 20,229 | 43,255,233 |
| Single householder, w/children | 18.3% | 17.1% | 15.8% |
| Single householder, no children | 11.3% | 7.6% | 10.8% |