| | Northfield, MN | Annandale, MN | United States |
| Population | 20,374 | 3,323 | 329,725,481 |
| Female Population | 51.6% | 55.3% | 50.5% |
| Male Population | 48.4% | 44.7% | 49.5% |
| Median Age | 28.5 | 43.1 | 38.4 |
| space3 | | | |
| Population - 2010 | 20,054 | 3,236 | 309,327,143 |
| Population - 2000 | 17,147 | 2,684 | 285,036,114 |
| Population - 1990 | 14,684 | 2,054 | 251,960,433 |
| Pop. 2000 to Now | 21.1% | 32.1% | 15.6% |
| Pop. 1990 to Now | 41.4% | 72.6% | 30.8% |
| space4 | | | |
| Population Density | 2,397.5 | 1,097.1 | 93.4 |
| Land Area | 8.5 | 3.0 | 3,531,905.4 |
| Water Area | 0.0 | 0.0 | 264,836.8 |
| space | | | |
| Est. Total Population By Age | | | |
| | Northfield, MN | Annandale, MN | United States |
| Age 0 to 4 | 3.8% | 4.1% | 5.9% |
| Age 5 to 9 | 4.0% | 7.6% | 6.1% |
| Age 10 to 14 | 5.7% | 7.8% | 6.6% |
| Age 15 to 17 | 3.0% | 3.8% | 3.9% |
| Age 18 to 20 | 20.0% | 3.9% | 4.0% |
| Age 21 to 24 | 11.8% | 3.9% | 5.2% |
| Age 25 to 34 | 7.5% | 8.7% | 13.8% |
| Age 35 to 44 | 9.7% | 15.4% | 12.9% |
| Age 45 to 54 | 9.8% | 9.0% | 12.6% |
| Age 55 to 59 | 4.5% | 5.2% | 6.7% |
| Age 60 to 64 | 5.3% | 5.3% | 6.3% |
| Age 65 to 74 | 8.2% | 11.6% | 9.6% |
| Age 75 to 84 | 4.5% | 11.0% | 4.5% |
| Age 85 and over | 2.3% | 2.6% | 1.9% |
| space1 | | | |
| Race | | | |
| | Northfield, MN | Annandale, MN | United States |
| White | 80.1% | 93.4% | 59.4% |
| Black | 2.4% | 0.1% | 12.2% |
| Asian | 4.4% | 0.8% | 5.6% |
| Native American | 0.1% | 0.0% | 0.6% |
| Hawaiian, Pacific Islander | 0.0% | 0.0% | 0.2% |
| Other | 0.0% | 0.0% | 0.4% |
| Two or More Races | 3.1% | 4.0% | 3.2% |
| Hispanic | 9.9% | 1.7% | 18.4% |
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| Marriage & Family | | | |
| | Northfield, MN | Annandale, MN | United States |
| Married Population | 37.8% | 52.9% | 49.8% |
| Currently Married | 36.8% | 52.4% | 48.0% |
| Married but Separated | 1.0% | 0.4% | 1.8% |
| Single Population | 62.2% | 47.1% | 50.2% |
| Never Married | 48.7% | 23.2% | 33.8% |
| Divorced | 8.7% | 15.5% | 10.8% |
| Widowed | 4.8% | 8.4% | 5.6% |
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| Household Size | 2.37 | 2.37 | 2.60 |
| Households | 6,198 | 1,374 | 124,010,992 |
| Family Households | 3,701 | 927 | 80,755,759 |
| Married couple, w/children | 32.5% | 25.4% | 30.5% |
| Married couple, no children | 49.0% | 51.9% | 42.9% |
| Non Family Households | 2,497 | 447 | 43,255,233 |
| Single householder, w/children | 12.0% | 16.8% | 15.8% |
| Single householder, no children | 6.5% | 5.9% | 10.8% |