| | Plymouth, MI | Geneva, IL | United States |
| Population | 9,308 | 21,472 | 329,725,481 |
| Female Population | 52.7% | 52.8% | 50.5% |
| Male Population | 47.3% | 47.2% | 49.5% |
| Median Age | 45.7 | 40.7 | 38.4 |
| space3 | | | |
| Population - 2010 | 9,117 | 21,613 | 309,327,143 |
| Population - 2000 | 9,022 | 19,515 | 285,036,114 |
| Population - 1990 | 9,560 | 12,617 | 251,960,433 |
| Pop. 2000 to Now | 1.3% | 11.1% | 15.6% |
| Pop. 1990 to Now | -4.4% | 71.8% | 30.8% |
| space4 | | | |
| Population Density | 4,208.0 | 2,169.3 | 93.4 |
| Land Area | 2.2 | 9.9 | 3,531,905.4 |
| Water Area | 0.0 | 0.2 | 264,836.8 |
| space | | | |
| Est. Total Population By Age | | | |
| | Plymouth, MI | Geneva, IL | United States |
| Age 0 to 4 | 4.0% | 4.1% | 5.9% |
| Age 5 to 9 | 6.0% | 8.2% | 6.1% |
| Age 10 to 14 | 5.0% | 8.1% | 6.6% |
| Age 15 to 17 | 5.4% | 5.0% | 3.9% |
| Age 18 to 20 | 2.4% | 3.5% | 4.0% |
| Age 21 to 24 | 3.9% | 3.7% | 5.2% |
| Age 25 to 34 | 11.3% | 9.3% | 13.8% |
| Age 35 to 44 | 11.1% | 13.7% | 12.9% |
| Age 45 to 54 | 18.8% | 13.3% | 12.6% |
| Age 55 to 59 | 9.5% | 9.7% | 6.7% |
| Age 60 to 64 | 6.7% | 6.5% | 6.3% |
| Age 65 to 74 | 8.7% | 9.7% | 9.6% |
| Age 75 to 84 | 4.8% | 4.3% | 4.5% |
| Age 85 and over | 2.3% | 0.9% | 1.9% |
| space1 | | | |
| Race | | | |
| | Plymouth, MI | Geneva, IL | United States |
| White | 92.3% | 84.8% | 59.4% |
| Black | 2.4% | 1.4% | 12.2% |
| Asian | 1.0% | 2.8% | 5.6% |
| Native American | 0.1% | 0.0% | 0.6% |
| Hawaiian, Pacific Islander | 0.0% | 0.0% | 0.2% |
| Other | 0.7% | 0.1% | 0.4% |
| Two or More Races | 2.6% | 2.2% | 3.2% |
| Hispanic | 1.0% | 8.8% | 18.4% |
| space2 | | | |
| Marriage & Family | | | |
| | Plymouth, MI | Geneva, IL | United States |
| Married Population | 49.5% | 59.5% | 49.8% |
| Currently Married | 49.1% | 59.0% | 48.0% |
| Married but Separated | 0.4% | 0.5% | 1.8% |
| Single Population | 50.5% | 40.5% | 50.2% |
| Never Married | 29.6% | 25.2% | 33.8% |
| Divorced | 13.5% | 9.9% | 10.8% |
| Widowed | 7.4% | 5.4% | 5.6% |
| space5 | | | |
| Household Size | 2.15 | 2.68 | 2.60 |
| Households | 4,207 | 7,964 | 124,010,992 |
| Family Households | 2,355 | 5,951 | 80,755,759 |
| Married couple, w/children | 40.0% | 37.5% | 30.5% |
| Married couple, no children | 38.3% | 45.3% | 42.9% |
| Non Family Households | 1,852 | 2,013 | 43,255,233 |
| Single householder, w/children | 12.1% | 10.1% | 15.8% |
| Single householder, no children | 9.6% | 7.2% | 10.8% |