Estimate, Median Age by Sex, Total Population (5-year estimate) in Johnson County, IA was 30.60000 Years of Age in January of 2022, according to the United States Federal Reserve. Historically, Estimate, Median Age by Sex, Total Population (5-year estimate) in Johnson County, IA reached a record high of 30.70000 in January of 2021 and a record low of 27.50000 in January of 2009. Trading Economics provides the current actual value, an historical data chart and related indicators for Estimate, Median Age by Sex, Total Population (5-year estimate) in Johnson County, IA - last updated from the United States Federal Reserve on May of 2024.