Books are often overlooked as a genealogical resource. Increasingly they can be researched online. The following helpful information comes from a Facebook posting by Susan Chappell of NSDAR Lineage Research:

In case you didn’t know: Other sources for online ebooks to search. Some require you create a free acct.

• www.ancestry.com  see “Card Catalog”
• www.familysearch.org   see “Search” “Books”
• https://archive.org/   see “Texts” and search for online books 
• http://books.google.com/   search family name + genealogy. Has over 20 million scanned books
• http://www.hathitrust.org/    is a partnership of academic & research institutions, offering a collection of millions of titles digitized from libraries around the world (search “genealogy”)
• https://about.jstor.org/   JSTOR provides access to more than 12 million academic journal articles, books, and primary sources in 75 disciplines. Good source for historic and genealogical journal articles.
• https://books.google.com/  Google Books is a service from Google Inc. that searches the full text of books and magazines that Google has scanned, converted to text using optical character recognition, and stored in its digital database.