| | Marengo, IN | Montgomery, IN | United States |
| Population | 732 | 1,060 | 329,725,481 |
| Female Population | 49.2% | 50.6% | 50.5% |
| Male Population | 50.8% | 49.4% | 49.5% |
| Median Age | 37.6 | 50.2 | 38.4 |
| space3 | | | |
| Population - 2010 | 825 | 731 | 309,327,143 |
| Population - 2000 | 829 | 368 | 285,036,114 |
| Population - 1990 | 856 | 351 | 251,960,433 |
| Pop. 2000 to Now | -2.5% | 107.6% | 15.6% |
| Pop. 1990 to Now | -5.6% | 117.7% | 30.8% |
| space4 | | | |
| Population Density | 945.7 | 4,398.3 | 93.4 |
| Land Area | 0.8 | 0.2 | 3,531,905.4 |
| Water Area | 0.0 | 0.0 | 264,836.8 |
| space | | | |
| Est. Total Population By Age | | | |
| | Marengo, IN | Montgomery, IN | United States |
| Age 0 to 4 | 6.6% | 5.7% | 5.9% |
| Age 5 to 9 | 8.2% | 3.8% | 6.1% |
| Age 10 to 14 | 3.7% | 2.5% | 6.6% |
| Age 15 to 17 | 3.3% | 5.0% | 3.9% |
| Age 18 to 20 | 6.1% | 0.9% | 4.0% |
| Age 21 to 24 | 4.9% | 5.7% | 5.2% |
| Age 25 to 34 | 15.3% | 13.0% | 13.8% |
| Age 35 to 44 | 12.2% | 9.3% | 12.9% |
| Age 45 to 54 | 12.0% | 11.3% | 12.6% |
| Age 55 to 59 | 5.7% | 15.5% | 6.7% |
| Age 60 to 64 | 6.0% | 10.3% | 6.3% |
| Age 65 to 74 | 7.7% | 12.5% | 9.6% |
| Age 75 to 84 | 5.1% | 3.5% | 4.5% |
| Age 85 and over | 3.3% | 1.0% | 1.9% |
| space1 | | | |
| Race | | | |
| | Marengo, IN | Montgomery, IN | United States |
| White | 92.8% | 98.9% | 59.4% |
| Black | 0.0% | 0.0% | 12.2% |
| Asian | 0.0% | 0.0% | 5.6% |
| Native American | 0.0% | 0.8% | 0.6% |
| Hawaiian, Pacific Islander | 0.0% | 0.0% | 0.2% |
| Other | 0.0% | 0.0% | 0.4% |
| Two or More Races | 1.8% | 0.0% | 3.2% |
| Hispanic | 5.5% | 0.3% | 18.4% |
| space2 | | | |
| Marriage & Family | | | |
| | Marengo, IN | Montgomery, IN | United States |
| Married Population | 50.4% | 69.1% | 49.8% |
| Currently Married | 49.6% | 69.1% | 48.0% |
| Married but Separated | 0.8% | 0.0% | 1.8% |
| Single Population | 49.6% | 30.9% | 50.2% |
| Never Married | 24.1% | 22.2% | 33.8% |
| Divorced | 17.4% | 5.0% | 10.8% |
| Widowed | 8.0% | 3.7% | 5.6% |
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| Household Size | 2.35 | 2.76 | 2.60 |
| Households | 311 | 384 | 124,010,992 |
| Family Households | 172 | 338 | 80,755,759 |
| Married couple, w/children | 19.8% | 30.2% | 30.5% |
| Married couple, no children | 59.9% | 50.3% | 42.9% |
| Non Family Households | 139 | 46 | 43,255,233 |
| Single householder, w/children | 16.9% | 5.6% | 15.8% |
| Single householder, no children | 3.5% | 13.9% | 10.8% |