| | Buffalo, IA | Milan, IL | United States |
| Population | 968 | 5,096 | 329,725,481 |
| Female Population | 48.0% | 49.5% | 50.5% |
| Male Population | 52.0% | 50.5% | 49.5% |
| Median Age | 45.4 | 39.2 | 38.4 |
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| Population - 2010 | 1,267 | 5,182 | 309,327,143 |
| Population - 2000 | 1,321 | 5,348 | 285,036,114 |
| Population - 1990 | 1,260 | 5,831 | 251,960,433 |
| Pop. 2000 to Now | -4.8% | -7.5% | 15.6% |
| Pop. 1990 to Now | -0.2% | -15.2% | 30.8% |
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| Population Density | 143.0 | 818.8 | 93.4 |
| Land Area | 6.8 | 6.2 | 3,531,905.4 |
| Water Area | 0.0 | 0.6 | 264,836.8 |
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| Est. Total Population By Age | | | |
| | Buffalo, IA | Milan, IL | United States |
| Age 0 to 4 | 2.8% | 9.4% | 5.9% |
| Age 5 to 9 | 4.9% | 4.9% | 6.1% |
| Age 10 to 14 | 6.3% | 4.6% | 6.6% |
| Age 15 to 17 | 4.8% | 1.8% | 3.9% |
| Age 18 to 20 | 2.9% | 1.5% | 4.0% |
| Age 21 to 24 | 1.8% | 6.5% | 5.2% |
| Age 25 to 34 | 9.9% | 14.4% | 13.8% |
| Age 35 to 44 | 16.1% | 11.8% | 12.9% |
| Age 45 to 54 | 11.8% | 11.4% | 12.6% |
| Age 55 to 59 | 12.5% | 5.3% | 6.7% |
| Age 60 to 64 | 7.4% | 7.2% | 6.3% |
| Age 65 to 74 | 12.5% | 13.1% | 9.6% |
| Age 75 to 84 | 4.9% | 5.8% | 4.5% |
| Age 85 and over | 1.6% | 2.4% | 1.9% |
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| Race | | | |
| | Buffalo, IA | Milan, IL | United States |
| White | 88.8% | 86.2% | 59.4% |
| Black | 0.3% | 2.5% | 12.2% |
| Asian | 1.0% | 2.4% | 5.6% |
| Native American | 0.0% | 0.0% | 0.6% |
| Hawaiian, Pacific Islander | 0.0% | 0.0% | 0.2% |
| Other | 6.3% | 0.0% | 0.4% |
| Two or More Races | 0.4% | 2.2% | 3.2% |
| Hispanic | 3.1% | 6.6% | 18.4% |
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| Marriage & Family | | | |
| | Buffalo, IA | Milan, IL | United States |
| Married Population | 38.7% | 43.0% | 49.8% |
| Currently Married | 37.1% | 42.3% | 48.0% |
| Married but Separated | 1.6% | 0.7% | 1.8% |
| Single Population | 61.3% | 57.0% | 50.2% |
| Never Married | 33.7% | 28.1% | 33.8% |
| Divorced | 16.8% | 19.3% | 10.8% |
| Widowed | 10.8% | 9.6% | 5.6% |
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| Household Size | 2.14 | 2.01 | 2.60 |
| Households | 453 | 2,532 | 124,010,992 |
| Family Households | 235 | 1,279 | 80,755,759 |
| Married couple, w/children | 29.4% | 25.3% | 30.5% |
| Married couple, no children | 29.8% | 41.8% | 42.9% |
| Non Family Households | 218 | 1,253 | 43,255,233 |
| Single householder, w/children | 21.7% | 21.4% | 15.8% |
| Single householder, no children | 19.1% | 11.5% | 10.8% |