Resident Population in Marion County, MO was 28.33600 Thous. of Persons in January of 2023, according to the United States Federal Reserve. Historically, Resident Population in Marion County, MO reached a record high of 28.95000 in January of 1983 and a record low of 27.63500 in January of 1989. Trading Economics provides the current actual value, an historical data chart and related indicators for Resident Population in Marion County, MO - last updated from the United States Federal Reserve on May of 2024.