Resident Population in Mercer County, MO was 3.46900 Thous. of Persons in January of 2023, according to the United States Federal Reserve. Historically, Resident Population in Mercer County, MO reached a record high of 4.91000 in January of 1970 and a record low of 3.43000 in January of 2007. Trading Economics provides the current actual value, an historical data chart and related indicators for Resident Population in Mercer County, MO - last updated from the United States Federal Reserve on May of 2024.