| | Thief River Falls, MN | Bemidji, MN | United States |
| Population | 8,791 | 15,114 | 329,725,481 |
| Female Population | 50.8% | 51.6% | 50.5% |
| Male Population | 49.2% | 48.4% | 49.5% |
| Median Age | 38.2 | 27.6 | 38.4 |
| space3 | | | |
| Population - 2010 | 8,641 | 14,289 | 309,327,143 |
| Population - 2000 | 8,410 | 11,917 | 285,036,114 |
| Population - 1990 | 8,010 | 11,245 | 251,960,433 |
| Pop. 2000 to Now | 3.3% | 29.7% | 15.6% |
| Pop. 1990 to Now | 8.5% | 37.4% | 30.8% |
| space4 | | | |
| Population Density | 1,555.1 | 1,054.3 | 93.4 |
| Land Area | 5.7 | 14.3 | 3,531,905.4 |
| Water Area | 0.2 | 4.9 | 264,836.8 |
| space | | | |
| Est. Total Population By Age | | | |
| | Thief River Falls, MN | Bemidji, MN | United States |
| Age 0 to 4 | 6.3% | 7.2% | 5.9% |
| Age 5 to 9 | 6.5% | 5.9% | 6.1% |
| Age 10 to 14 | 4.9% | 4.6% | 6.6% |
| Age 15 to 17 | 4.1% | 2.5% | 3.9% |
| Age 18 to 20 | 3.6% | 12.7% | 4.0% |
| Age 21 to 24 | 4.9% | 12.6% | 5.2% |
| Age 25 to 34 | 15.1% | 12.7% | 13.8% |
| Age 35 to 44 | 11.8% | 10.3% | 12.9% |
| Age 45 to 54 | 9.8% | 6.4% | 12.6% |
| Age 55 to 59 | 6.3% | 5.0% | 6.7% |
| Age 60 to 64 | 7.1% | 4.1% | 6.3% |
| Age 65 to 74 | 9.9% | 8.1% | 9.6% |
| Age 75 to 84 | 6.6% | 5.1% | 4.5% |
| Age 85 and over | 3.1% | 2.9% | 1.9% |
| space1 | | | |
| Race | | | |
| | Thief River Falls, MN | Bemidji, MN | United States |
| White | 88.4% | 75.3% | 59.4% |
| Black | 2.0% | 1.2% | 12.2% |
| Asian | 0.5% | 1.5% | 5.6% |
| Native American | 1.3% | 8.8% | 0.6% |
| Hawaiian, Pacific Islander | 0.0% | 0.1% | 0.2% |
| Other | 0.3% | 0.0% | 0.4% |
| Two or More Races | 1.7% | 10.3% | 3.2% |
| Hispanic | 5.8% | 2.7% | 18.4% |
| space2 | | | |
| Marriage & Family | | | |
| | Thief River Falls, MN | Bemidji, MN | United States |
| Married Population | 45.1% | 29.4% | 49.8% |
| Currently Married | 44.3% | 28.6% | 48.0% |
| Married but Separated | 0.7% | 0.8% | 1.8% |
| Single Population | 54.9% | 70.6% | 50.2% |
| Never Married | 34.1% | 50.7% | 33.8% |
| Divorced | 12.8% | 13.7% | 10.8% |
| Widowed | 8.1% | 6.2% | 5.6% |
| space5 | | | |
| Household Size | 2.14 | 2.11 | 2.60 |
| Households | 3,995 | 6,346 | 124,010,992 |
| Family Households | 2,060 | 2,755 | 80,755,759 |
| Married couple, w/children | 28.0% | 28.7% | 30.5% |
| Married couple, no children | 46.7% | 33.4% | 42.9% |
| Non Family Households | 1,935 | 3,591 | 43,255,233 |
| Single householder, w/children | 20.3% | 28.0% | 15.8% |
| Single householder, no children | 5.0% | 9.9% | 10.8% |