Libraries are great sources for researchers, but they're not the be-all-end-all they once were. A website called Project Gutenberg has over 45,000 free e-books to offer. Most are classics, but some are somewhat esoteric.
Bartleby.com is an excellent resource for literature, and possibly is or was associated with Columbia University.
You can also get a huge amount of 19th and 20th century non-fiction reference books, periodicals, and other texts from the various on-line university sites at Internet Archive.
History research in volumes specific to the area and time periods if you're looking for historical references, there's none better. For example, The Genealogical Guide to Early American Settlers, Volumes 1-3 and The History of Allegheny county, Pa, Volumes 1-2.
You can read these works on line, or download pdf versions which can then be read or searched for specific names or words. Also, more than 1 million books ~ from classic 19th century fiction and current novels to technical guides and research materials are available in the specially designed format to support those who are blind, dyslexic or are otherwise visually impaired.
And of course, www.unz.org is one of my favorite archives, that starts with The Abolistionist and ends with Yank Magazine. All issues are downloadable. And there are hundreds of magazines, books, video and films.
Amazon also offers many public domain books free in the Kindle format, and many others at a nominal fee.