Oregon Heritage Commission — Clatsop County History Publications. Maps, illustrations, photos, surveys, and much more. Some of these publications are digitized. Others may be available through interlibrary loan or at the Clatsop County Historical Society.
Restore Oregon (formerly the Historic Preservation League of Oregon) — nice, multi-purpose list of relevant resources to help determine significance.
Clatsop County Historical Society digital archive — The Clatsop County Historical Society maintains an Archive and Research Library in the Heritage Museum documenting Clatsop County History. Many of their print artifacts are digitally available here.
The Building Technology Heritage Library (BTHL) is primarily a collection of American and Canadian, pre-1964 architectural trade catalogs, house plan books, and technical building guides. Trade catalogs are an important primary source to document past design and construction practices.
The Ted Natt Library of the Columbia River Maritime Museum contains more than 12,500 books, periodicals, logs, ledgers, videos, manuscripts, photo albums, and other ephemera relating to local, regional, and international maritime topics, including 33,000 photos. It is open Monday and Wednesday from 1:00 to 5:00 pm or by appointment.
JSTOR — This powerful collection provides access to full-text academic journal articles, books, and primary sources. Includes Oregon Historical Quarterly from 1897 through 2018. JSTOR also includes journals such as APT Bulletin: The Journal of Preservation Technology, Architectural History, Building Material, Built Environment, Construction History, Future Anterior: Journal of Historic Preservation, History, Theory, and Criticism, The Pacific Northwest Quarterly, Traditional Dwellings and Settlements Review, etc.