Guidelines for the development of library service in Washington County, Oregon, are provided in this report. The demographic characteristics of Washington County are discussed briefly with emphasis on the approximately 125,000 people without direct access to library service. A comprehensive plan for coooerative countywide library service is proposed. The plan includes provisions for legal and financial support necessary to develop and sustain the service. Proposed programs include: (1) books by mail; (2) courier service; (3) countywide borrowing privileges for all county residents; (4) information, reference, and research service; (5) film service; (6) cassette service; and (7) bookmobile service. A schedule for implementation of the plan and a proposed budget are provided. Over 100 references are listed. (PF)