| | Clay, KY | Willmar, MN | United States |
| Population | 1,088 | 20,823 | 329,725,481 |
| Female Population | 49.9% | 51.6% | 50.5% |
| Male Population | 50.1% | 48.4% | 49.5% |
| Median Age | 33.2 | 34.2 | 38.4 |
| space3 | | | |
| Population - 2010 | 1,175 | 19,580 | 309,327,143 |
| Population - 2000 | 1,179 | 18,351 | 285,036,114 |
| Population - 1990 | 1,173 | 17,531 | 251,960,433 |
| Pop. 2000 to Now | -7.5% | 8.4% | 15.6% |
| Pop. 1990 to Now | -7.0% | 13.5% | 30.8% |
| space4 | | | |
| Population Density | 1,262.2 | 1,490.4 | 93.4 |
| Land Area | 0.9 | 14.0 | 3,531,905.4 |
| Water Area | 0.0 | 1.3 | 264,836.8 |
| space | | | |
| Est. Total Population By Age | | | |
| | Clay, KY | Willmar, MN | United States |
| Age 0 to 4 | 6.0% | 7.8% | 5.9% |
| Age 5 to 9 | 2.6% | 7.5% | 6.1% |
| Age 10 to 14 | 5.4% | 7.6% | 6.6% |
| Age 15 to 17 | 2.2% | 3.4% | 3.9% |
| Age 18 to 20 | 4.7% | 4.8% | 4.0% |
| Age 21 to 24 | 13.4% | 5.6% | 5.2% |
| Age 25 to 34 | 17.6% | 14.4% | 13.8% |
| Age 35 to 44 | 6.6% | 11.5% | 12.9% |
| Age 45 to 54 | 13.2% | 9.9% | 12.6% |
| Age 55 to 59 | 7.4% | 5.7% | 6.7% |
| Age 60 to 64 | 6.6% | 5.6% | 6.3% |
| Age 65 to 74 | 8.5% | 9.2% | 9.6% |
| Age 75 to 84 | 4.9% | 3.4% | 4.5% |
| Age 85 and over | 0.9% | 3.5% | 1.9% |
| space1 | | | |
| Race | | | |
| | Clay, KY | Willmar, MN | United States |
| White | 98.9% | 61.6% | 59.4% |
| Black | 0.0% | 11.1% | 12.2% |
| Asian | 0.0% | 1.1% | 5.6% |
| Native American | 0.0% | 0.6% | 0.6% |
| Hawaiian, Pacific Islander | 0.0% | 0.0% | 0.2% |
| Other | 0.0% | 0.2% | 0.4% |
| Two or More Races | 0.3% | 2.1% | 3.2% |
| Hispanic | 0.8% | 23.4% | 18.4% |
| space2 | | | |
| Marriage & Family | | | |
| | Clay, KY | Willmar, MN | United States |
| Married Population | 34.8% | 47.4% | 49.8% |
| Currently Married | 31.8% | 46.5% | 48.0% |
| Married but Separated | 3.0% | 0.9% | 1.8% |
| Single Population | 65.2% | 52.6% | 50.2% |
| Never Married | 41.5% | 37.0% | 33.8% |
| Divorced | 14.5% | 9.3% | 10.8% |
| Widowed | 9.2% | 6.3% | 5.6% |
| space5 | | | |
| Household Size | 2.60 | 2.56 | 2.60 |
| Households | 418 | 7,775 | 124,010,992 |
| Family Households | 219 | 4,857 | 80,755,759 |
| Married couple, w/children | 21.0% | 27.9% | 30.5% |
| Married couple, no children | 40.6% | 43.0% | 42.9% |
| Non Family Households | 199 | 2,918 | 43,255,233 |
| Single householder, w/children | 22.4% | 20.2% | 15.8% |
| Single householder, no children | 16.0% | 9.0% | 10.8% |