| | Flossmoor, IL | New Lenox, IL | United States |
| Population | 9,868 | 26,942 | 329,725,481 |
| Female Population | 52.9% | 48.8% | 50.5% |
| Male Population | 47.2% | 51.2% | 49.5% |
| Median Age | 43 | 36.6 | 38.4 |
| space3 | | | |
| Population - 2010 | 9,421 | 24,344 | 309,327,143 |
| Population - 2000 | 9,301 | 17,771 | 285,036,114 |
| Population - 1990 | 8,651 | 9,627 | 251,960,433 |
| Pop. 2000 to Now | -3.0% | 52.4% | 15.6% |
| Pop. 1990 to Now | 4.2% | 181.4% | 30.8% |
| space4 | | | |
| Population Density | 2,695.4 | 1,737.8 | 93.4 |
| Land Area | 3.7 | 15.5 | 3,531,905.4 |
| Water Area | 0.0 | 0.0 | 264,836.8 |
| space | | | |
| Est. Total Population By Age | | | |
| | Flossmoor, IL | New Lenox, IL | United States |
| Age 0 to 4 | 7.9% | 8.8% | 5.9% |
| Age 5 to 9 | 6.7% | 6.7% | 6.1% |
| Age 10 to 14 | 6.2% | 8.3% | 6.6% |
| Age 15 to 17 | 5.2% | 5.3% | 3.9% |
| Age 18 to 20 | 4.8% | 3.4% | 4.0% |
| Age 21 to 24 | 2.0% | 3.8% | 5.2% |
| Age 25 to 34 | 5.8% | 10.2% | 13.8% |
| Age 35 to 44 | 12.7% | 16.7% | 12.9% |
| Age 45 to 54 | 16.0% | 13.0% | 12.6% |
| Age 55 to 59 | 7.1% | 8.6% | 6.7% |
| Age 60 to 64 | 8.2% | 4.5% | 6.3% |
| Age 65 to 74 | 12.2% | 7.0% | 9.6% |
| Age 75 to 84 | 3.2% | 2.6% | 4.5% |
| Age 85 and over | 2.1% | 1.2% | 1.9% |
| space1 | | | |
| Race | | | |
| | Flossmoor, IL | New Lenox, IL | United States |
| White | 28.6% | 91.3% | 59.4% |
| Black | 64.1% | 0.6% | 12.2% |
| Asian | 1.9% | 0.6% | 5.6% |
| Native American | 0.0% | 0.0% | 0.6% |
| Hawaiian, Pacific Islander | 0.0% | 0.0% | 0.2% |
| Other | 0.1% | 0.1% | 0.4% |
| Two or More Races | 3.6% | 2.8% | 3.2% |
| Hispanic | 1.6% | 4.6% | 18.4% |
| space2 | | | |
| Marriage & Family | | | |
| | Flossmoor, IL | New Lenox, IL | United States |
| Married Population | 59.7% | 65.9% | 49.8% |
| Currently Married | 57.8% | 65.2% | 48.0% |
| Married but Separated | 1.8% | 0.6% | 1.8% |
| Single Population | 40.3% | 34.1% | 50.2% |
| Never Married | 26.9% | 24.6% | 33.8% |
| Divorced | 8.2% | 5.4% | 10.8% |
| Widowed | 5.2% | 4.1% | 5.6% |
| space5 | | | |
| Household Size | 2.79 | 2.98 | 2.60 |
| Households | 3,519 | 9,007 | 124,010,992 |
| Family Households | 2,621 | 7,375 | 80,755,759 |
| Married couple, w/children | 37.6% | 47.7% | 30.5% |
| Married couple, no children | 45.9% | 41.0% | 42.9% |
| Non Family Households | 898 | 1,632 | 43,255,233 |
| Single householder, w/children | 13.7% | 6.4% | 15.8% |
| Single householder, no children | 2.7% | 4.9% | 10.8% |