| | Johnston, IA | Asbury, IA | United States |
| Population | 20,871 | 5,291 | 321,418,820 |
| Population - 2010 | 15,723 | 3,852 | 308,745,538 |
| Population - 2000 | 8,649 | 2,450 | 285,036,114 |
| Population - 1990 | 4,702 | 2,013 | 251,960,433 |
| Pop. 1990 to Now | 343.88% | 162.84% | 27.57% |
| Pop. 2000 to Now | 141.31% | 115.96% | 12.76% |
| Pop. Density | 1,217 | 1,640 | 91 |
| Land Area | 17 | 3 | 3,531,905 |
| Water Area | 1 | 0 | 264,837 |
| Median Age | 38.1 | 34.5 | 37.4 |
| Female Population | 52.38% | 50.85% | 50.81% |
| Male Population | 47.62% | 49.15% | 49.19% |
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| EST. TOTAL POPULATION BY AGE | | | |
| | Johnston, IA | Asbury, IA | United States |
| Age 0 to 4 | 6.80% | 9.41% | 6.36% |
| Age 5 to 9 | 6.45% | 9.08% | 6.51% |
| Age 10 to 14 | 8.58% | 9.94% | 6.59% |
| Age 15 to 17 | 6.23% | 6.23% | 4.03% |
| Age 18 to 20 | 2.51% | 3.49% | 4.35% |
| Age 21 to 24 | 2.12% | 2.52% | 5.61% |
| Age 25 to 34 | 13.11% | 10.31% | 13.47% |
| Age 35 to 44 | 17.54% | 13.78% | 12.97% |
| Age 45 to 54 | 13.56% | 14.44% | 14.09% |
| Age 55 to 59 | 6.00% | 6.39% | 6.57% |
| Age 60 to 64 | 6.48% | 4.91% | 5.72% |
| Age 65 to 74 | 6.85% | 6.37% | 7.64% |
| Age 75 to 84 | 2.66% | 2.93% | 4.26% |
| Age 85 and over | 1.13% | 0.21% | 1.85% |
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| RACE | | | |
| | Johnston, IA | Asbury, IA | United States |
| White | 91.54% | 85.93% | 62.77% |
| Black | 1.11% | 3.59% | 12.24% |
| Asian | 3.82% | 6.87% | 4.95% |
| Native American | 0.22% | 0.00% | 0.66% |
| Hawaiian, Pacific Islander | 0.30% | 0.00% | 0.16% |
| Other | 0.05% | 0.00% | 0.20% |
| Two or More Races | 0.65% | 0.70% | 2.13% |
| Hispanic | 2.31% | 2.91% | 16.90% |
| Non-Hispanic | 97.69% | 97.09% | 83.10% |
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| FAMILY | | | |
| | Johnston, IA | Asbury, IA | United States |
| Households | 7,211 | 1,559 | 116,211,000 |
| Family Households | 5,227 | 1,308 | 76,958,100 |
| Non Family Households | 1,984 | 251 | 39,253,000 |
| Household Size | 2.58 | 3.11 | 2.63 |
| Married Population | 64.15% | 68.10% | 50.58% |
| Single Population | 35.85% | 31.90% | 49.42% |
| Now Married | 63.16% | 68.10% | 48.41% |
| Married but Separated | 0.99% | 0.00% | 2.17% |
| Never Married | 24.34% | 21.59% | 32.55% |
| Widowed | 3.12% | 3.26% | 5.95% |
| Divorced | 8.38% | 7.06% | 10.92% |
| Married, w/children | 46.59% | 50.23% | 31.68% |
| Married, no children | 39.76% | 38.07% | 41.44% |
| Single, w/children | 10.18% | 8.72% | 16.94% |
| Single, no children | 3.48% | 2.98% | 9.95% |