Resident Population in St. Clair County, MI was 159.87400 Thous. of Persons in January of 2023, according to the United States Federal Reserve. Historically, Resident Population in St. Clair County, MI reached a record high of 170.23600 in January of 2006 and a record low of 119.28000 in January of 1970. Trading Economics provides the current actual value, an historical data chart and related indicators for Resident Population in St. Clair County, MI - last updated from the United States Federal Reserve on May of 2024.