Resident Population in Cass County, IL was 12.59600 Thous. of Persons in January of 2023, according to the United States Federal Reserve. Historically, Resident Population in Cass County, IL reached a record high of 15.10000 in January of 1981 and a record low of 12.14100 in January of 2019. Trading Economics provides the current actual value, an historical data chart and related indicators for Resident Population in Cass County, IL - last updated from the United States Federal Reserve on May of 2024.