Resident Population in Whiteside County, IL was 54.49800 Thous. of Persons in January of 2023, according to the United States Federal Reserve. Historically, Resident Population in Whiteside County, IL reached a record high of 66.30000 in January of 1979 and a record low of 54.49800 in January of 2023. Trading Economics provides the current actual value, an historical data chart and related indicators for Resident Population in Whiteside County, IL - last updated from the United States Federal Reserve on May of 2024.