Click on Research our Records to access the National Archives Catalog. Search in the box provided. You can then limit to online items only or limit by using the facets at the left side of the page. A multi-volume paper guide is also available in the reference collection at call number: CD3026 1995. Also available digitally in the database HeinOnline and as a searchable web version on the NARA website. The NARA website version is updated regularly. Researchers may also want to consult the guide to pre-federal records in the reference collection at call number CD3045.W441989.
The major research library for Congress and for the United States in general. American Memory is the online website for the digital collections of the Library of Congress. Use the catalog at this link to find additional collections.
Information on collections at smaller repositories. No longer a separate database. Records are added to WorldCat. The earlier paper volumes included all repositories, regardless of size. See: CD3022.N37 (available in Hodges and in Special Collections)