Resident Population in McClain County, OK was 47.07200 Thous. of Persons in January of 2023, according to the United States Federal Reserve. Historically, Resident Population in McClain County, OK reached a record high of 47.07200 in January of 2023 and a record low of 14.15700 in January of 1970. Trading Economics provides the current actual value, an historical data chart and related indicators for Resident Population in McClain County, OK - last updated from the United States Federal Reserve on May of 2024.