Four important multivolume reference sources on American (U.S.) biography that are indexed in Biography and Genealogy Master Index Online, are in the collections of the Andover-Harvard Theological Library (call numbers noted), several other Harvard libraries, and in many public and academic libraries:
American National Biography (1999), Dictionary of American Biography (1928-1936, plus supplements), and Notable American Women cite published and archival resources; their entries are written by named scholars and researchers.
If you have a valid Harvard ID and PIN number or you are in a Harvard library, you may access American National Biography Online; entries from the Dictionary of American Biography are online in Biography in Context.
You may also want to search The African American Biographical Database (AABD), which brings together in one resource the biographies of thousands of African Americans, 1790-1950. These biographical sketches have been assembled from the series Black Biographical Dictionaries and from other biographical dictionaries and sources.
If you are not a Harvard Library patron, check for the availability of these reference sources in your local library.
For more information, contact a research librarian.