Resident Population in Washington County, MD was 157.22800 Thous. of Persons in January of 2024, according to the United States Federal Reserve. Historically, Resident Population in Washington County, MD reached a record high of 157.22800 in January of 2024 and a record low of 103.82900 in January of 1970. Trading Economics provides the current actual value, an historical data chart and related indicators for Resident Population in Washington County, MD - last updated from the United States Federal Reserve on April of 2026.