| | Peru, IL | Princeton, IL | United States |
| Population | 9,862 | 7,750 | 329,725,481 |
| Female Population | 53.0% | 54.2% | 50.5% |
| Male Population | 47.0% | 45.8% | 49.5% |
| Median Age | 47.4 | 48.7 | 38.4 |
| space3 | | | |
| Population - 2010 | 10,320 | 7,919 | 309,327,143 |
| Population - 2000 | 9,835 | 7,501 | 285,036,114 |
| Population - 1990 | 9,302 | 7,197 | 251,960,433 |
| Pop. 2000 to Now | -2.3% | -1.3% | 15.6% |
| Pop. 1990 to Now | 3.3% | 2.9% | 30.8% |
| space4 | | | |
| Population Density | 1,043.5 | 964.1 | 93.4 |
| Land Area | 9.5 | 8.0 | 3,531,905.4 |
| Water Area | 0.1 | 0.0 | 264,836.8 |
| space | | | |
| Est. Total Population By Age | | | |
| | Peru, IL | Princeton, IL | United States |
| Age 0 to 4 | 5.8% | 4.5% | 5.9% |
| Age 5 to 9 | 6.9% | 4.8% | 6.1% |
| Age 10 to 14 | 5.2% | 6.5% | 6.6% |
| Age 15 to 17 | 3.2% | 2.9% | 3.9% |
| Age 18 to 20 | 1.8% | 2.2% | 4.0% |
| Age 21 to 24 | 3.6% | 3.7% | 5.2% |
| Age 25 to 34 | 11.9% | 12.6% | 13.8% |
| Age 35 to 44 | 10.1% | 8.0% | 12.9% |
| Age 45 to 54 | 11.4% | 13.0% | 12.6% |
| Age 55 to 59 | 9.4% | 6.9% | 6.7% |
| Age 60 to 64 | 6.4% | 6.7% | 6.3% |
| Age 65 to 74 | 11.8% | 14.8% | 9.6% |
| Age 75 to 84 | 7.2% | 9.9% | 4.5% |
| Age 85 and over | 5.4% | 3.4% | 1.9% |
| space1 | | | |
| Race | | | |
| | Peru, IL | Princeton, IL | United States |
| White | 88.9% | 93.2% | 59.4% |
| Black | 1.2% | 0.1% | 12.2% |
| Asian | 0.9% | 1.1% | 5.6% |
| Native American | 0.0% | 0.0% | 0.6% |
| Hawaiian, Pacific Islander | 0.0% | 0.0% | 0.2% |
| Other | 0.0% | 1.2% | 0.4% |
| Two or More Races | 1.9% | 1.7% | 3.2% |
| Hispanic | 7.1% | 2.7% | 18.4% |
| space2 | | | |
| Marriage & Family | | | |
| | Peru, IL | Princeton, IL | United States |
| Married Population | 53.9% | 51.1% | 49.8% |
| Currently Married | 53.2% | 50.0% | 48.0% |
| Married but Separated | 0.7% | 1.1% | 1.8% |
| Single Population | 46.1% | 48.9% | 50.2% |
| Never Married | 24.4% | 22.1% | 33.8% |
| Divorced | 10.8% | 17.3% | 10.8% |
| Widowed | 10.9% | 9.6% | 5.6% |
| space5 | | | |
| Household Size | 2.21 | 2.13 | 2.60 |
| Households | 4,361 | 3,547 | 124,010,992 |
| Family Households | 2,818 | 2,010 | 80,755,759 |
| Married couple, w/children | 23.4% | 25.5% | 30.5% |
| Married couple, no children | 51.1% | 54.6% | 42.9% |
| Non Family Households | 1,543 | 1,537 | 43,255,233 |
| Single householder, w/children | 21.7% | 15.8% | 15.8% |
| Single householder, no children | 3.8% | 4.1% | 10.8% |