Estimate, Median Age by Sex, Total Population (5-year estimate) in Marion County, IA was 39.80000 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 Marion County, IA reached a record high of 39.80000 in January of 2022 and a record low of 38.60000 in January of 2011. 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 Marion County, IA - last updated from the United States Federal Reserve on May of 2024.