Washington County is in Tallgrass Prairie Kansas. Of the 105 counties in the Jayhawk State, Washington County ranks 30th in terms of size (898 square miles). Browse all Washington County ranches for sale on the Land Network to find the ranch that's right for your business or commercial needs, from the sprawling legacy ranch to unbelievable residential ranch for your second home, investment property or retirement nest egg. The most common type of land for sale by combined acreage in Washington County is recreational property.