This is a link
http://www2.newpaltz.edu/~hathaway/washsq.html
to an e-text version of the novel.
Washington Square was first published
http://cdl.library.cornell.edu/moa/browse.author/j.14.html
in Harper's in serialized form. This site provides direct links to the pages of Harper's electronic archive where James' work is located. The image of the printed page is reproducedwith the original font, illustrations, and advertisements.
The Henry James Review
http://muse.jhu.edu/demo/henry_james_review/
is an academic journal that published academic essays and reviews of academic books regarding Henry James and his works. A few articles are available online for free for anyone. Most universities and libraries have access to the entire Review. The Review is also available in print form and there is a table of contents that includes all of the essays that have been printed in the Review.
This site is called the Henry James Scholar's Guide to Web Sites.
http://www2.newpaltz.edu/~hathaway/#aboutjames
It offers links to websites covering a very wide range of information. One link offers a collection of film reviews of the 1997 movie version of Washington Square. Another link offers a comprehensive bibliography of the leading essays published on the novel.