| | Willoughby, OH | Mayfield Heights, OH | United States |
| Population | 23,753 | 20,113 | 329,725,481 |
| Female Population | 54.4% | 53.4% | 50.5% |
| Male Population | 45.6% | 46.6% | 49.5% |
| Median Age | 44 | 38.6 | 38.4 |
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| Population - 2010 | 22,259 | 19,124 | 309,327,143 |
| Population - 2000 | 22,621 | 19,386 | 285,036,114 |
| Population - 1990 | 20,510 | 19,847 | 251,960,433 |
| Pop. 2000 to Now | 1.5% | -5.2% | 15.6% |
| Pop. 1990 to Now | 12.0% | -7.4% | 30.8% |
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| Population Density | 2,317.6 | 4,823.3 | 93.4 |
| Land Area | 10.2 | 4.2 | 3,531,905.4 |
| Water Area | 0.1 | 0.0 | 264,836.8 |
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| Est. Total Population By Age | | | |
| | Willoughby, OH | Mayfield Heights, OH | United States |
| Age 0 to 4 | 4.0% | 6.4% | 5.9% |
| Age 5 to 9 | 5.1% | 4.7% | 6.1% |
| Age 10 to 14 | 4.7% | 5.4% | 6.6% |
| Age 15 to 17 | 3.6% | 2.2% | 3.9% |
| Age 18 to 20 | 2.6% | 2.0% | 4.0% |
| Age 21 to 24 | 4.4% | 4.2% | 5.2% |
| Age 25 to 34 | 16.4% | 18.5% | 13.8% |
| Age 35 to 44 | 10.6% | 15.1% | 12.9% |
| Age 45 to 54 | 11.3% | 10.1% | 12.6% |
| Age 55 to 59 | 9.2% | 6.3% | 6.7% |
| Age 60 to 64 | 6.3% | 3.6% | 6.3% |
| Age 65 to 74 | 11.9% | 10.2% | 9.6% |
| Age 75 to 84 | 6.2% | 7.5% | 4.5% |
| Age 85 and over | 3.8% | 3.8% | 1.9% |
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| Race | | | |
| | Willoughby, OH | Mayfield Heights, OH | United States |
| White | 89.4% | 68.8% | 59.4% |
| Black | 5.7% | 15.1% | 12.2% |
| Asian | 1.1% | 4.2% | 5.6% |
| Native American | 0.0% | 0.0% | 0.6% |
| Hawaiian, Pacific Islander | 0.0% | 0.0% | 0.2% |
| Other | 0.3% | 0.3% | 0.4% |
| Two or More Races | 2.2% | 5.5% | 3.2% |
| Hispanic | 1.4% | 6.1% | 18.4% |
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| Marriage & Family | | | |
| | Willoughby, OH | Mayfield Heights, OH | United States |
| Married Population | 42.9% | 44.3% | 49.8% |
| Currently Married | 42.5% | 43.5% | 48.0% |
| Married but Separated | 0.4% | 0.9% | 1.8% |
| Single Population | 57.1% | 55.7% | 50.2% |
| Never Married | 36.5% | 30.3% | 33.8% |
| Divorced | 12.9% | 17.4% | 10.8% |
| Widowed | 7.7% | 7.9% | 5.6% |
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| Household Size | 2.07 | 2.00 | 2.60 |
| Households | 11,322 | 9,983 | 124,010,992 |
| Family Households | 5,912 | 4,901 | 80,755,759 |
| Married couple, w/children | 23.5% | 34.6% | 30.5% |
| Married couple, no children | 46.6% | 35.8% | 42.9% |
| Non Family Households | 5,410 | 5,082 | 43,255,233 |
| Single householder, w/children | 15.7% | 15.3% | 15.8% |
| Single householder, no children | 14.1% | 14.3% | 10.8% |