George A. Smith recalls between 100-200 people knew about the plural marriage revelation in Nauvoo.
George A. Smith, "Discourse by President George A. Smith," August 13, 1871, in Journal of Discourses, 26 vols. (Liverpool: Albert Carrington; London: Latter-day Saints' Book Depot, 1872): 213–214
In 1843 the law on celestial marriage was written, but not published, and was known only to perhaps one or two hundred persons. It was written from the dictation of Joseph Smith, by Elder William Clayton, his private secretary, who is now in this city. This revelation was published in 1852, read to a general conference, and accepted as a portion of the faith of the Church.