| | Libby, MT | Key West, FL | United States |
| Population | 2,745 | 26,776 | 329,725,481 |
| Female Population | 50.1% | 47.0% | 50.5% |
| Male Population | 49.9% | 53.0% | 49.5% |
| Median Age | 50.1 | 44.2 | 38.4 |
| space3 | | | |
| Population - 2010 | 2,631 | 24,662 | 309,327,143 |
| Population - 2000 | 2,626 | 25,478 | 285,036,114 |
| Population - 1990 | 2,532 | 24,832 | 251,960,433 |
| Pop. 2000 to Now | 8.3% | -6.7% | 15.6% |
| Pop. 1990 to Now | 12.4% | -4.3% | 30.8% |
| space4 | | | |
| Population Density | 1,465.6 | 4,790.0 | 93.4 |
| Land Area | 1.9 | 5.6 | 3,531,905.4 |
| Water Area | 0.0 | 1.6 | 264,836.8 |
| space | | | |
| Est. Total Population By Age | | | |
| | Libby, MT | Key West, FL | United States |
| Age 0 to 4 | 4.9% | 4.0% | 5.9% |
| Age 5 to 9 | 3.1% | 3.5% | 6.1% |
| Age 10 to 14 | 2.8% | 4.6% | 6.6% |
| Age 15 to 17 | 6.6% | 2.3% | 3.9% |
| Age 18 to 20 | 4.4% | 2.5% | 4.0% |
| Age 21 to 24 | 3.9% | 3.4% | 5.2% |
| Age 25 to 34 | 8.2% | 15.5% | 13.8% |
| Age 35 to 44 | 10.5% | 15.4% | 12.9% |
| Age 45 to 54 | 14.6% | 13.3% | 12.6% |
| Age 55 to 59 | 6.7% | 9.4% | 6.7% |
| Age 60 to 64 | 8.8% | 7.3% | 6.3% |
| Age 65 to 74 | 9.3% | 12.0% | 9.6% |
| Age 75 to 84 | 10.9% | 4.8% | 4.5% |
| Age 85 and over | 5.2% | 2.0% | 1.9% |
| space1 | | | |
| Race | | | |
| | Libby, MT | Key West, FL | United States |
| White | 83.7% | 58.9% | 59.4% |
| Black | 0.4% | 12.3% | 12.2% |
| Asian | 0.5% | 1.7% | 5.6% |
| Native American | 4.5% | 0.1% | 0.6% |
| Hawaiian, Pacific Islander | 0.0% | 0.0% | 0.2% |
| Other | 0.0% | 0.2% | 0.4% |
| Two or More Races | 4.8% | 2.1% | 3.2% |
| Hispanic | 6.1% | 24.7% | 18.4% |
| space2 | | | |
| Marriage & Family | | | |
| | Libby, MT | Key West, FL | United States |
| Married Population | 45.0% | 45.1% | 49.8% |
| Currently Married | 42.2% | 43.0% | 48.0% |
| Married but Separated | 2.8% | 2.1% | 1.8% |
| Single Population | 55.0% | 54.9% | 50.2% |
| Never Married | 31.9% | 34.1% | 33.8% |
| Divorced | 12.0% | 16.0% | 10.8% |
| Widowed | 11.1% | 4.8% | 5.6% |
| space5 | | | |
| Household Size | 1.94 | 2.32 | 2.60 |
| Households | 1,354 | 11,002 | 124,010,992 |
| Family Households | 665 | 5,748 | 80,755,759 |
| Married couple, w/children | 21.2% | 23.7% | 30.5% |
| Married couple, no children | 60.9% | 55.2% | 42.9% |
| Non Family Households | 689 | 5,254 | 43,255,233 |
| Single householder, w/children | 16.2% | 14.3% | 15.8% |
| Single householder, no children | 1.7% | 6.8% | 10.8% |