Resident Population in Williamson County, TX was 697.19100 Thous. of Persons in January of 2023, according to the United States Federal Reserve. Historically, Resident Population in Williamson County, TX reached a record high of 697.19100 in January of 2023 and a record low of 37.30500 in January of 1970. Trading Economics provides the current actual value, an historical data chart and related indicators for Resident Population in Williamson County, TX - last updated from the United States Federal Reserve on May of 2024.