Resident Population in Douglas County, IL was 19.62900 Thous. of Persons in January of 2023, according to the United States Federal Reserve. Historically, Resident Population in Douglas County, IL reached a record high of 20.20000 in January of 1976 and a record low of 18.90000 in January of 1971. Trading Economics provides the current actual value, an historical data chart and related indicators for Resident Population in Douglas County, IL - last updated from the United States Federal Reserve on May of 2024.