This is a list of the large digitized collections that are free and open to all to access. Almost every institution has some of their collections located online. Consider searching for smaller collections, in addition to larger collections.
Finding primary sources is a multi-step process. There is no "one-stop-shop" database that will give you everything you need for your paper. Follow these tips:
When searching for primary source collections online, include the following additional phrases with your keywords:
Be aware that digital collections only show a small portion of what an institution holds!