Resident Population in Washington County, KS was 5.50400 Thous. of Persons in January of 2023, according to the United States Federal Reserve. Historically, Resident Population in Washington County, KS reached a record high of 9.24900 in January of 1970 and a record low of 5.44900 in January of 2019. Trading Economics provides the current actual value, an historical data chart and related indicators for Resident Population in Washington County, KS - last updated from the United States Federal Reserve on May of 2024.