What is a Special District?
Special districts are a form of local government. They are created by their constituents to meet specific service needs for their communities. Most perform a single function such as water delivery, fire protection, wastewater or cemetery maintenance, to name a few. Some, like county service districts, provide multiple services.
Read More on the Special Districts Association of Oregon Website

This map shows where SDAO membes are located in Oregon. From the SDAO website