| | St. Charles, IA | Norwalk, IA | United States |
| Population | 713 | 12,592 | 329,725,481 |
| Female Population | 55.8% | 51.7% | 50.5% |
| Male Population | 44.2% | 48.4% | 49.5% |
| Median Age | 38.7 | 36 | 38.4 |
| space3 | | | |
| Population - 2010 | 682 | 9,046 | 309,327,143 |
| Population - 2000 | 619 | 6,884 | 285,036,114 |
| Population - 1990 | 537 | 5,726 | 251,960,433 |
| Pop. 2000 to Now | 6.0% | 80.8% | 15.6% |
| Pop. 1990 to Now | 22.2% | 117.4% | 30.8% |
| space4 | | | |
| Population Density | 1,327.8 | 1,101.8 | 93.4 |
| Land Area | 0.5 | 11.4 | 3,531,905.4 |
| Water Area | 0.0 | 0.4 | 264,836.8 |
| space | | | |
| Est. Total Population By Age | | | |
| | St. Charles, IA | Norwalk, IA | United States |
| Age 0 to 4 | 7.3% | 6.3% | 5.9% |
| Age 5 to 9 | 2.0% | 7.4% | 6.1% |
| Age 10 to 14 | 7.2% | 11.0% | 6.6% |
| Age 15 to 17 | 5.9% | 4.2% | 3.9% |
| Age 18 to 20 | 6.3% | 1.8% | 4.0% |
| Age 21 to 24 | 2.9% | 3.9% | 5.2% |
| Age 25 to 34 | 16.0% | 13.8% | 13.8% |
| Age 35 to 44 | 8.1% | 14.8% | 12.9% |
| Age 45 to 54 | 14.4% | 12.4% | 12.6% |
| Age 55 to 59 | 4.9% | 6.4% | 6.7% |
| Age 60 to 64 | 5.9% | 6.5% | 6.3% |
| Age 65 to 74 | 11.5% | 6.3% | 9.6% |
| Age 75 to 84 | 5.9% | 3.5% | 4.5% |
| Age 85 and over | 1.7% | 1.8% | 1.9% |
| space1 | | | |
| Race | | | |
| | St. Charles, IA | Norwalk, IA | United States |
| White | 98.6% | 94.1% | 59.4% |
| Black | 0.4% | 1.3% | 12.2% |
| Asian | 0.0% | 0.5% | 5.6% |
| Native American | 0.0% | 0.0% | 0.6% |
| Hawaiian, Pacific Islander | 0.0% | 0.0% | 0.2% |
| Other | 0.0% | 0.1% | 0.4% |
| Two or More Races | 0.4% | 2.1% | 3.2% |
| Hispanic | 0.6% | 1.9% | 18.4% |
| space2 | | | |
| Marriage & Family | | | |
| | St. Charles, IA | Norwalk, IA | United States |
| Married Population | 53.9% | 58.1% | 49.8% |
| Currently Married | 53.4% | 57.2% | 48.0% |
| Married but Separated | 0.5% | 0.9% | 1.8% |
| Single Population | 46.1% | 41.9% | 50.2% |
| Never Married | 26.5% | 24.0% | 33.8% |
| Divorced | 12.8% | 13.9% | 10.8% |
| Widowed | 6.9% | 3.9% | 5.6% |
| space5 | | | |
| Household Size | 2.36 | 2.59 | 2.60 |
| Households | 302 | 4,818 | 124,010,992 |
| Family Households | 188 | 3,200 | 80,755,759 |
| Married couple, w/children | 28.7% | 45.0% | 30.5% |
| Married couple, no children | 54.8% | 36.1% | 42.9% |
| Non Family Households | 114 | 1,618 | 43,255,233 |
| Single householder, w/children | 16.5% | 15.1% | 15.8% |
| Single householder, no children | 0.0% | 3.8% | 10.8% |