Primary sources are foundational. They include: first-hand accounts, letters, diaries offer insights on period dialogue and attitudes, memoirs, maps, legal documents including wills, deeds, court rolls, treaties etc., which can also give a sense of language and attitudes of the time. Then there are judicial reports, school log books, ships’ logs, local newspapers, transcripts of old court cases, journals, advertisements, photographs, cookbooks, etiquette manuals, dictionaries of the time. Civil and military records.
Another excellent article, with lots of ideas for your research. If you write historical fiction and aren’t already following this blog, you should be!