Resident Population in Piatt County, IL was 16.71400 Thous. of Persons in January of 2023, according to the United States Federal Reserve. Historically, Resident Population in Piatt County, IL reached a record high of 16.78100 in January of 2021 and a record low of 15.50900 in January of 1970. Trading Economics provides the current actual value, an historical data chart and related indicators for Resident Population in Piatt County, IL - last updated from the United States Federal Reserve on May of 2024.