| | Polk City, IA | Nevada, IA | United States |
| Population | 5,386 | 7,017 | 329,725,481 |
| Female Population | 44.7% | 48.2% | 50.5% |
| Male Population | 55.3% | 51.8% | 49.5% |
| Median Age | 35.5 | 40.3 | 38.4 |
| space3 | | | |
| Population - 2010 | 3,452 | 6,811 | 309,327,143 |
| Population - 2000 | 2,344 | 6,658 | 285,036,114 |
| Population - 1990 | 1,908 | 6,009 | 251,960,433 |
| Pop. 2000 to Now | 119.3% | 0.4% | 15.6% |
| Pop. 1990 to Now | 169.4% | 11.2% | 30.8% |
| space4 | | | |
| Population Density | 1,057.3 | 1,231.9 | 93.4 |
| Land Area | 5.1 | 5.7 | 3,531,905.4 |
| Water Area | 0.1 | 0.0 | 264,836.8 |
| space | | | |
| Est. Total Population By Age | | | |
| | Polk City, IA | Nevada, IA | United States |
| Age 0 to 4 | 8.1% | 4.0% | 5.9% |
| Age 5 to 9 | 10.6% | 9.8% | 6.1% |
| Age 10 to 14 | 7.4% | 8.0% | 6.6% |
| Age 15 to 17 | 2.3% | 4.1% | 3.9% |
| Age 18 to 20 | 3.4% | 3.0% | 4.0% |
| Age 21 to 24 | 0.7% | 3.0% | 5.2% |
| Age 25 to 34 | 15.9% | 12.1% | 13.8% |
| Age 35 to 44 | 18.0% | 13.3% | 12.9% |
| Age 45 to 54 | 17.1% | 10.3% | 12.6% |
| Age 55 to 59 | 4.8% | 5.5% | 6.7% |
| Age 60 to 64 | 3.7% | 9.9% | 6.3% |
| Age 65 to 74 | 6.1% | 10.2% | 9.6% |
| Age 75 to 84 | 1.9% | 5.0% | 4.5% |
| Age 85 and over | 0.0% | 1.8% | 1.9% |
| space1 | | | |
| Race | | | |
| | Polk City, IA | Nevada, IA | United States |
| White | 97.8% | 90.2% | 59.4% |
| Black | 0.6% | 0.7% | 12.2% |
| Asian | 0.0% | 0.0% | 5.6% |
| Native American | 0.0% | 0.0% | 0.6% |
| Hawaiian, Pacific Islander | 0.0% | 0.0% | 0.2% |
| Other | 0.0% | 0.4% | 0.4% |
| Two or More Races | 0.9% | 1.8% | 3.2% |
| Hispanic | 0.7% | 7.0% | 18.4% |
| space2 | | | |
| Marriage & Family | | | |
| | Polk City, IA | Nevada, IA | United States |
| Married Population | 75.0% | 53.5% | 49.8% |
| Currently Married | 73.5% | 51.6% | 48.0% |
| Married but Separated | 1.5% | 1.9% | 1.8% |
| Single Population | 25.1% | 46.5% | 50.2% |
| Never Married | 17.1% | 26.1% | 33.8% |
| Divorced | 5.3% | 14.4% | 10.8% |
| Widowed | 2.7% | 6.0% | 5.6% |
| space5 | | | |
| Household Size | 2.86 | 2.23 | 2.60 |
| Households | 1,868 | 3,083 | 124,010,992 |
| Family Households | 1,518 | 1,762 | 80,755,759 |
| Married couple, w/children | 55.7% | 33.9% | 30.5% |
| Married couple, no children | 39.6% | 40.9% | 42.9% |
| Non Family Households | 350 | 1,321 | 43,255,233 |
| Single householder, w/children | 2.4% | 19.9% | 15.8% |
| Single householder, no children | 2.3% | 5.3% | 10.8% |