| | Montgomery, IL | Gainesville, GA | United States |
| Population | 20,084 | 41,730 | 329,725,481 |
| Female Population | 46.6% | 53.4% | 50.5% |
| Male Population | 53.4% | 46.6% | 49.5% |
| Median Age | 30.8 | 32.4 | 38.4 |
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| Population - 2010 | 18,385 | 34,066 | 309,327,143 |
| Population - 2000 | 5,471 | 25,578 | 285,036,114 |
| Population - 1990 | 4,267 | 17,885 | 251,960,433 |
| Pop. 2000 to Now | 268.9% | 72.9% | 15.6% |
| Pop. 1990 to Now | 373.0% | 147.2% | 30.8% |
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| Population Density | 2,168.9 | 1,273.3 | 93.4 |
| Land Area | 9.3 | 32.8 | 3,531,905.4 |
| Water Area | 0.2 | 1.9 | 264,836.8 |
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| Est. Total Population By Age | | | |
| | Montgomery, IL | Gainesville, GA | United States |
| Age 0 to 4 | 6.3% | 7.2% | 5.9% |
| Age 5 to 9 | 7.6% | 7.8% | 6.1% |
| Age 10 to 14 | 9.2% | 6.4% | 6.6% |
| Age 15 to 17 | 8.4% | 5.1% | 3.9% |
| Age 18 to 20 | 5.6% | 4.8% | 4.0% |
| Age 21 to 24 | 5.5% | 6.8% | 5.2% |
| Age 25 to 34 | 13.0% | 15.4% | 13.8% |
| Age 35 to 44 | 17.0% | 12.2% | 12.9% |
| Age 45 to 54 | 11.9% | 10.7% | 12.6% |
| Age 55 to 59 | 5.7% | 4.9% | 6.7% |
| Age 60 to 64 | 3.3% | 4.0% | 6.3% |
| Age 65 to 74 | 3.8% | 9.2% | 9.6% |
| Age 75 to 84 | 2.0% | 3.4% | 4.5% |
| Age 85 and over | 0.6% | 2.1% | 1.9% |
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| Race | | | |
| | Montgomery, IL | Gainesville, GA | United States |
| White | 64.6% | 40.2% | 59.4% |
| Black | 3.8% | 16.0% | 12.2% |
| Asian | 0.8% | 2.7% | 5.6% |
| Native American | 0.0% | 0.0% | 0.6% |
| Hawaiian, Pacific Islander | 0.2% | 0.0% | 0.2% |
| Other | 0.0% | 0.8% | 0.4% |
| Two or More Races | 1.5% | 2.2% | 3.2% |
| Hispanic | 29.1% | 38.1% | 18.4% |
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| Marriage & Family | | | |
| | Montgomery, IL | Gainesville, GA | United States |
| Married Population | 50.3% | 44.6% | 49.8% |
| Currently Married | 49.4% | 42.0% | 48.0% |
| Married but Separated | 0.9% | 2.6% | 1.8% |
| Single Population | 49.7% | 55.4% | 50.2% |
| Never Married | 37.5% | 38.8% | 33.8% |
| Divorced | 8.7% | 11.7% | 10.8% |
| Widowed | 3.6% | 4.8% | 5.6% |
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| Household Size | 3.14 | 2.78 | 2.60 |
| Households | 6,390 | 14,619 | 124,010,992 |
| Family Households | 4,679 | 9,307 | 80,755,759 |
| Married couple, w/children | 47.6% | 32.1% | 30.5% |
| Married couple, no children | 32.9% | 31.9% | 42.9% |
| Non Family Households | 1,711 | 5,312 | 43,255,233 |
| Single householder, w/children | 13.4% | 22.8% | 15.8% |
| Single householder, no children | 6.2% | 13.2% | 10.8% |