| | Fairfield, ID | Sweetwater, ID | United States |
| Population | 493 | 269 | 329,725,481 |
| Female Population | 66.7% | 39.4% | 50.5% |
| Male Population | 33.3% | 60.6% | 49.5% |
| Median Age | 35.5 | 46.5 | 38.4 |
| space3 | | | |
| Population - 2010 | 415 | 106 | 309,327,143 |
| Population - 2000 | 395 | 136 | 285,036,114 |
| Population - 1990 | 371 | 121 | 251,960,433 |
| Pop. 2000 to Now | 2.0% | 102.9% | 15.6% |
| Pop. 1990 to Now | 8.6% | 128.1% | 30.8% |
| space4 | | | |
| Population Density | 562.8 | 225.7 | 93.4 |
| Land Area | 0.9 | 1.2 | 3,531,905.4 |
| Water Area | 0.0 | 0.0 | 264,836.8 |
| space | | | |
| Est. Total Population By Age | | | |
| | Fairfield, ID | Sweetwater, ID | United States |
| Age 0 to 4 | 4.5% | 7.8% | 5.9% |
| Age 5 to 9 | 15.0% | 7.8% | 6.1% |
| Age 10 to 14 | 8.5% | 5.9% | 6.6% |
| Age 15 to 17 | 3.0% | 6.7% | 3.9% |
| Age 18 to 20 | 4.3% | 0.0% | 4.0% |
| Age 21 to 24 | 0.0% | 2.2% | 5.2% |
| Age 25 to 34 | 13.6% | 2.2% | 13.8% |
| Age 35 to 44 | 29.0% | 11.5% | 12.9% |
| Age 45 to 54 | 5.1% | 32.0% | 12.6% |
| Age 55 to 59 | 4.7% | 1.5% | 6.7% |
| Age 60 to 64 | 2.8% | 11.9% | 6.3% |
| Age 65 to 74 | 2.4% | 5.2% | 9.6% |
| Age 75 to 84 | 6.3% | 5.2% | 4.5% |
| Age 85 and over | 0.8% | 0.0% | 1.9% |
| space1 | | | |
| Race | | | |
| | Fairfield, ID | Sweetwater, ID | United States |
| White | 93.3% | 30.5% | 59.4% |
| Black | 0.0% | 0.0% | 12.2% |
| Asian | 0.0% | 0.0% | 5.6% |
| Native American | 0.0% | 46.1% | 0.6% |
| Hawaiian, Pacific Islander | 0.0% | 0.0% | 0.2% |
| Other | 0.0% | 0.0% | 0.4% |
| Two or More Races | 2.6% | 23.4% | 3.2% |
| Hispanic | 4.1% | 0.0% | 18.4% |
| space2 | | | |
| Marriage & Family | | | |
| | Fairfield, ID | Sweetwater, ID | United States |
| Married Population | 28.2% | 71.6% | 49.8% |
| Currently Married | 28.2% | 71.6% | 48.0% |
| Married but Separated | 0.0% | 0.0% | 1.8% |
| Single Population | 71.8% | 28.4% | 50.2% |
| Never Married | 26.5% | 11.4% | 33.8% |
| Divorced | 41.4% | 17.1% | 10.8% |
| Widowed | 3.9% | 0.0% | 5.6% |
| space5 | | | |
| Household Size | 4.07 | 3.74 | 2.60 |
| Households | 121 | 72 | 124,010,992 |
| Family Households | 54 | 61 | 80,755,759 |
| Married couple, w/children | 51.9% | 32.8% | 30.5% |
| Married couple, no children | 37.0% | 42.6% | 42.9% |
| Non Family Households | 67 | 11 | 43,255,233 |
| Single householder, w/children | 11.1% | 18.0% | 15.8% |
| Single householder, no children | 0.0% | 6.6% | 10.8% |