Resident Population in Monroe County, IL was 34.95700 Thous. of Persons in January of 2023, according to the United States Federal Reserve. Historically, Resident Population in Monroe County, IL reached a record high of 35.03300 in January of 2022 and a record low of 18.30000 in January of 1971. Trading Economics provides the current actual value, an historical data chart and related indicators for Resident Population in Monroe County, IL - last updated from the United States Federal Reserve on May of 2024.