| | Cotati, CA | Johnston, IA | United States |
| Population | 7,603 | 23,418 | 329,725,481 |
| Female Population | 53.5% | 50.8% | 50.5% |
| Male Population | 46.5% | 49.2% | 49.5% |
| Median Age | 37.2 | 37.7 | 38.4 |
| space3 | | | |
| Population - 2010 | 7,286 | 17,388 | 309,327,143 |
| Population - 2000 | 6,471 | 8,649 | 285,036,114 |
| Population - 1990 | 5,714 | 4,702 | 251,960,433 |
| Pop. 2000 to Now | 15.2% | 167.0% | 15.6% |
| Pop. 1990 to Now | 30.4% | 391.1% | 30.8% |
| space4 | | | |
| Population Density | 4,044.2 | 1,397.7 | 93.4 |
| Land Area | 1.9 | 16.8 | 3,531,905.4 |
| Water Area | 0.0 | 1.5 | 264,836.8 |
| space | | | |
| Est. Total Population By Age | | | |
| | Cotati, CA | Johnston, IA | United States |
| Age 0 to 4 | 6.9% | 7.1% | 5.9% |
| Age 5 to 9 | 8.0% | 8.6% | 6.1% |
| Age 10 to 14 | 4.3% | 8.1% | 6.6% |
| Age 15 to 17 | 2.1% | 5.0% | 3.9% |
| Age 18 to 20 | 3.5% | 1.7% | 4.0% |
| Age 21 to 24 | 6.1% | 3.7% | 5.2% |
| Age 25 to 34 | 15.6% | 12.1% | 13.8% |
| Age 35 to 44 | 16.0% | 13.5% | 12.9% |
| Age 45 to 54 | 10.7% | 14.1% | 12.6% |
| Age 55 to 59 | 4.7% | 7.0% | 6.7% |
| Age 60 to 64 | 7.9% | 4.3% | 6.3% |
| Age 65 to 74 | 8.5% | 9.1% | 9.6% |
| Age 75 to 84 | 4.9% | 3.9% | 4.5% |
| Age 85 and over | 0.8% | 2.0% | 1.9% |
| space1 | | | |
| Race | | | |
| | Cotati, CA | Johnston, IA | United States |
| White | 71.2% | 78.3% | 59.4% |
| Black | 1.0% | 9.9% | 12.2% |
| Asian | 2.0% | 6.5% | 5.6% |
| Native American | 0.0% | 0.1% | 0.6% |
| Hawaiian, Pacific Islander | 0.2% | 0.0% | 0.2% |
| Other | 0.3% | 0.0% | 0.4% |
| Two or More Races | 6.8% | 2.1% | 3.2% |
| Hispanic | 18.6% | 3.2% | 18.4% |
| space2 | | | |
| Marriage & Family | | | |
| | Cotati, CA | Johnston, IA | United States |
| Married Population | 50.1% | 60.7% | 49.8% |
| Currently Married | 49.5% | 59.4% | 48.0% |
| Married but Separated | 0.7% | 1.2% | 1.8% |
| Single Population | 49.9% | 39.3% | 50.2% |
| Never Married | 32.5% | 25.1% | 33.8% |
| Divorced | 13.3% | 9.3% | 10.8% |
| Widowed | 4.1% | 4.9% | 5.6% |
| space5 | | | |
| Household Size | 2.68 | 2.50 | 2.60 |
| Households | 2,828 | 9,256 | 124,010,992 |
| Family Households | 1,670 | 6,298 | 80,755,759 |
| Married couple, w/children | 38.4% | 37.4% | 30.5% |
| Married couple, no children | 33.8% | 44.1% | 42.9% |
| Non Family Households | 1,158 | 2,958 | 43,255,233 |
| Single householder, w/children | 13.9% | 16.4% | 15.8% |
| Single householder, no children | 13.8% | 2.1% | 10.8% |