| | Avon, SD | Four Corners, MT | United States |
| Population | 735 | 5,649 | 329,725,481 |
| Female Population | 47.4% | 47.4% | 50.5% |
| Male Population | 52.7% | 52.6% | 49.5% |
| Median Age | 36.2 | 35.1 | 38.4 |
| space3 | | | |
| Population - 2010 | 590 | 2,837 | 309,327,143 |
| Population - 2000 | 561 | 1,828 | 285,036,114 |
| Population - 1990 | 576 | 1,536 | 251,960,433 |
| Pop. 2000 to Now | 4.1% | 156.2% | 15.6% |
| Pop. 1990 to Now | 1.4% | 204.9% | 30.8% |
| space4 | | | |
| Population Density | 1,137.8 | 528.7 | 93.4 |
| Land Area | 0.6 | 10.7 | 3,531,905.4 |
| Water Area | 0.0 | 0.1 | 264,836.8 |
| space | | | |
| Est. Total Population By Age | | | |
| | Avon, SD | Four Corners, MT | United States |
| Age 0 to 4 | 4.4% | 9.2% | 5.9% |
| Age 5 to 9 | 7.5% | 10.1% | 6.1% |
| Age 10 to 14 | 16.9% | 10.7% | 6.6% |
| Age 15 to 17 | 6.3% | 2.7% | 3.9% |
| Age 18 to 20 | 1.2% | 1.5% | 4.0% |
| Age 21 to 24 | 1.5% | 2.2% | 5.2% |
| Age 25 to 34 | 10.1% | 13.4% | 13.8% |
| Age 35 to 44 | 12.0% | 16.6% | 12.9% |
| Age 45 to 54 | 6.9% | 13.8% | 12.6% |
| Age 55 to 59 | 7.2% | 4.4% | 6.7% |
| Age 60 to 64 | 6.7% | 4.8% | 6.3% |
| Age 65 to 74 | 12.0% | 7.5% | 9.6% |
| Age 75 to 84 | 4.8% | 2.9% | 4.5% |
| Age 85 and over | 2.7% | 0.3% | 1.9% |
| space1 | | | |
| Race | | | |
| | Avon, SD | Four Corners, MT | United States |
| White | 94.4% | 89.7% | 59.4% |
| Black | 0.0% | 2.0% | 12.2% |
| Asian | 0.0% | 0.0% | 5.6% |
| Native American | 2.9% | 0.0% | 0.6% |
| Hawaiian, Pacific Islander | 0.0% | 0.0% | 0.2% |
| Other | 0.0% | 0.0% | 0.4% |
| Two or More Races | 0.5% | 4.4% | 3.2% |
| Hispanic | 2.2% | 3.9% | 18.4% |
| space2 | | | |
| Marriage & Family | | | |
| | Avon, SD | Four Corners, MT | United States |
| Married Population | 67.9% | 60.0% | 49.8% |
| Currently Married | 66.4% | 59.8% | 48.0% |
| Married but Separated | 1.5% | 0.2% | 1.8% |
| Single Population | 32.1% | 40.0% | 50.2% |
| Never Married | 25.0% | 19.6% | 33.8% |
| Divorced | 1.3% | 14.7% | 10.8% |
| Widowed | 5.7% | 5.8% | 5.6% |
| space5 | | | |
| Household Size | 2.70 | 2.65 | 2.60 |
| Households | 272 | 2,135 | 124,010,992 |
| Family Households | 188 | 1,348 | 80,755,759 |
| Married couple, w/children | 26.1% | 53.9% | 30.5% |
| Married couple, no children | 64.4% | 31.8% | 42.9% |
| Non Family Households | 84 | 787 | 43,255,233 |
| Single householder, w/children | 8.0% | 11.1% | 15.8% |
| Single householder, no children | 1.6% | 3.1% | 10.8% |