Resident Population in St. Louis County, MO was 992.92900 Thous. of Persons in January of 2024, according to the United States Federal Reserve. Historically, Resident Population in St. Louis County, MO reached a record high of 1018.01500 in January of 1997 and a record low of 947.00000 in January of 1972. Trading Economics provides the current actual value, an historical data chart and related indicators for Resident Population in St. Louis County, MO - last updated from the United States Federal Reserve on April of 2026.