There was a total of nearly $800,000 of land and rural real estate for sale in Washington County, Illinois, recently on Land.com. The total of all Washington County farms and rural real estate for sale was almost 1,000 acres. Washington County ranks 98th in Illinois for the combined amount of land currently advertised for sale. Okawville had the most land for sale. Washington County is Illinois's 46th largest county (563 square miles). It's located in the Southern Illinois region of the state.