| | Amelia, OH | Fairfield, OH | United States |
| Population | 11,795 | 44,550 | 329,725,481 |
| Female Population | 50.7% | 52.3% | 50.5% |
| Male Population | 49.3% | 47.7% | 49.5% |
| Median Age | 33.9 | 39.7 | 38.4 |
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| Population - 2010 | 4,786 | 42,556 | 309,327,143 |
| Population - 2000 | 2,752 | 42,097 | 285,036,114 |
| Population - 1990 | 1,837 | 39,729 | 251,960,433 |
| Pop. 2000 to Now | 92.9% | 1.2% | 15.6% |
| Pop. 1990 to Now | 189.0% | 7.2% | 30.8% |
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| Population Density | 6,582.0 | 2,130.6 | 93.4 |
| Land Area | 1.8 | 20.9 | 3,531,905.4 |
| Water Area | 0.0 | 0.1 | 264,836.8 |
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| Est. Total Population By Age | | | |
| | Amelia, OH | Fairfield, OH | United States |
| Age 0 to 4 | 10.3% | 6.5% | 5.9% |
| Age 5 to 9 | 8.9% | 5.1% | 6.1% |
| Age 10 to 14 | 3.4% | 6.5% | 6.6% |
| Age 15 to 17 | 1.8% | 4.2% | 3.9% |
| Age 18 to 20 | 3.1% | 3.3% | 4.0% |
| Age 21 to 24 | 5.1% | 5.0% | 5.2% |
| Age 25 to 34 | 19.2% | 12.9% | 13.8% |
| Age 35 to 44 | 13.5% | 13.0% | 12.9% |
| Age 45 to 54 | 12.8% | 11.2% | 12.6% |
| Age 55 to 59 | 4.2% | 7.7% | 6.7% |
| Age 60 to 64 | 5.2% | 7.6% | 6.3% |
| Age 65 to 74 | 6.8% | 9.6% | 9.6% |
| Age 75 to 84 | 5.3% | 4.3% | 4.5% |
| Age 85 and over | 0.4% | 2.9% | 1.9% |
| space1 | | | |
| Race | | | |
| | Amelia, OH | Fairfield, OH | United States |
| White | 94.4% | 66.6% | 59.4% |
| Black | 1.3% | 15.7% | 12.2% |
| Asian | 0.0% | 5.6% | 5.6% |
| Native American | 0.0% | 0.0% | 0.6% |
| Hawaiian, Pacific Islander | 0.0% | 0.0% | 0.2% |
| Other | 0.3% | 1.2% | 0.4% |
| Two or More Races | 0.9% | 3.8% | 3.2% |
| Hispanic | 3.1% | 7.1% | 18.4% |
| space2 | | | |
| Marriage & Family | | | |
| | Amelia, OH | Fairfield, OH | United States |
| Married Population | 52.4% | 49.7% | 49.8% |
| Currently Married | 49.2% | 48.7% | 48.0% |
| Married but Separated | 3.2% | 1.1% | 1.8% |
| Single Population | 47.6% | 50.3% | 50.2% |
| Never Married | 28.5% | 29.1% | 33.8% |
| Divorced | 12.0% | 13.7% | 10.8% |
| Widowed | 7.1% | 7.4% | 5.6% |
| space5 | | | |
| Household Size | 2.40 | 2.40 | 2.60 |
| Households | 4,915 | 18,342 | 124,010,992 |
| Family Households | 2,786 | 11,730 | 80,755,759 |
| Married couple, w/children | 43.7% | 29.9% | 30.5% |
| Married couple, no children | 33.1% | 42.4% | 42.9% |
| Non Family Households | 2,129 | 6,612 | 43,255,233 |
| Single householder, w/children | 10.3% | 16.6% | 15.8% |
| Single householder, no children | 12.9% | 11.0% | 10.8% |