Resident Population in Jefferson County, IA was 15.44000 Thous. of Persons in January of 2023, according to the United States Federal Reserve. Historically, Resident Population in Jefferson County, IA reached a record high of 18.18000 in January of 2019 and a record low of 14.60000 in January of 1974. Trading Economics provides the current actual value, an historical data chart and related indicators for Resident Population in Jefferson County, IA - last updated from the United States Federal Reserve on May of 2024.