Book collection named after U of I Regent Jerome J. Day, whose donated collection of western Americana was the basis for creating this collection.

General and project correspondence, research reports, project reports, laboratory notebooks, photographs, procedures manuals, accessions lists, minutes, and other records chiefly relating to research by Potlatch in Lewiston, Idaho, and by the Washington State University College of Engineering, and to the Potlatch Forests Information Center.