| | Fenton, MO | Rock Springs, WY | United States |
| Population | 4,000 | 23,505 | 329,725,481 |
| Female Population | 48.6% | 48.8% | 50.5% |
| Male Population | 51.5% | 51.2% | 49.5% |
| Median Age | 49.6 | 34.7 | 38.4 |
| space3 | | | |
| Population - 2010 | 4,023 | 23,017 | 309,327,143 |
| Population - 2000 | 4,360 | 18,708 | 285,036,114 |
| Population - 1990 | 3,346 | 19,050 | 251,960,433 |
| Pop. 2000 to Now | -7.6% | 22.6% | 15.6% |
| Pop. 1990 to Now | 20.4% | 20.4% | 30.8% |
| space4 | | | |
| Population Density | 642.7 | 1,213.1 | 93.4 |
| Land Area | 6.2 | 19.4 | 3,531,905.4 |
| Water Area | 0.3 | 0.0 | 264,836.8 |
| space | | | |
| Est. Total Population By Age | | | |
| | Fenton, MO | Rock Springs, WY | United States |
| Age 0 to 4 | 4.9% | 6.8% | 5.9% |
| Age 5 to 9 | 5.4% | 9.0% | 6.1% |
| Age 10 to 14 | 5.0% | 6.6% | 6.6% |
| Age 15 to 17 | 3.7% | 3.7% | 3.9% |
| Age 18 to 20 | 4.7% | 4.3% | 4.0% |
| Age 21 to 24 | 5.5% | 6.1% | 5.2% |
| Age 25 to 34 | 7.9% | 14.0% | 13.8% |
| Age 35 to 44 | 9.2% | 15.1% | 12.9% |
| Age 45 to 54 | 18.4% | 10.4% | 12.6% |
| Age 55 to 59 | 7.6% | 6.1% | 6.7% |
| Age 60 to 64 | 6.8% | 6.3% | 6.3% |
| Age 65 to 74 | 13.4% | 7.9% | 9.6% |
| Age 75 to 84 | 4.0% | 2.5% | 4.5% |
| Age 85 and over | 3.6% | 1.2% | 1.9% |
| space1 | | | |
| Race | | | |
| | Fenton, MO | Rock Springs, WY | United States |
| White | 85.1% | 77.8% | 59.4% |
| Black | 4.2% | 2.0% | 12.2% |
| Asian | 0.9% | 1.2% | 5.6% |
| Native American | 0.0% | 0.9% | 0.6% |
| Hawaiian, Pacific Islander | 0.0% | 0.0% | 0.2% |
| Other | 0.0% | 0.7% | 0.4% |
| Two or More Races | 9.1% | 2.2% | 3.2% |
| Hispanic | 0.7% | 15.2% | 18.4% |
| space2 | | | |
| Marriage & Family | | | |
| | Fenton, MO | Rock Springs, WY | United States |
| Married Population | 64.8% | 49.8% | 49.8% |
| Currently Married | 62.2% | 47.8% | 48.0% |
| Married but Separated | 2.6% | 2.0% | 1.8% |
| Single Population | 35.2% | 50.2% | 50.2% |
| Never Married | 24.1% | 30.0% | 33.8% |
| Divorced | 5.7% | 13.9% | 10.8% |
| Widowed | 5.4% | 6.3% | 5.6% |
| space5 | | | |
| Household Size | 2.64 | 2.71 | 2.60 |
| Households | 1,501 | 8,564 | 124,010,992 |
| Family Households | 1,186 | 5,312 | 80,755,759 |
| Married couple, w/children | 32.9% | 40.2% | 30.5% |
| Married couple, no children | 52.4% | 36.2% | 42.9% |
| Non Family Households | 315 | 3,252 | 43,255,233 |
| Single householder, w/children | 1.9% | 14.9% | 15.8% |
| Single householder, no children | 12.7% | 8.6% | 10.8% |