Fawn M. Brodie lists 48 plural wives of Joseph's, including women sealed to Joseph posthumously.
Fawn M. Brodie, No Man Knows My History: The Life of Joseph Smith, 2nd rev. ed. (New York, NY: Knopf, 1971), 457–488
[Brodie provides an appendix in her biography of Joseph Smith listing the women she believes were plural wives of Joseph Smith; she includes women who were sealed to JS while he was alive and posthumous sealings for a total of 48 women.]