1833 - Joseph Smith (Age: 27) married Fanny Alger (Age: 16).
"Benjamin Johnson, a close friend of Joseph Smith, described Fanny as, “varry nice and comly, [to whom] everyone Seemed partial for the ameability of her character.” She is generally considered the first plural wife of Joseph Smith. Although undocumented, the marriage of Fanny and Joseph most likely took place in Kirtland, Ohio sometime in 1833. She would have been sixteen years old. At the time, Fanny was living in the Smith home, perhaps helping Emma with house work and the children. Ann Eliza Webb recalls, “Mrs. Smith had an adopted daughter, a very pretty, pleasing young girl, about seventeen years old. She was extremely fond of her; no mother could be more devoted, and their affection for each other was a constant object of remark, so absorbing and genuine did it seem”"((Mormon Polygamy: A History pg 5; In Sacred Loneliness: The Plural Wives of Joseph Smith pgs 25,26,34; Mormon Enigma: Emma Hale Smith pg 66)
"Joseph kept his marriage to Fanny out of the view of the public, and his wife Emma. Chauncey Webb recounts Emma’s later discovery of the relationship: “Emma was furious, and drove the girl, who was unable to conceal the consequences of her celestial relation with the prophet, out of her house”. Ann Eliza again recalls: “...it was felt that [Emma] certainly must have had some very good reason for her action. By degrees it became whispered about that Joseph’s love for his adopted daughter was by no means a paternal affection, and his wife, discovering the fact, at once took measures to place the girl beyond his reach...Since Emma refused decidedly to allow her to remain in her house...my mother offered to take her until she could be sent to her relatives...”" ((In Sacred Loneliness: The Plural Wives of Joseph Smith pgs 34,35)
"Book of Mormon witness, Oliver Cowdery, felt the relationship was something other than a marriage. He referred to it as “A dirty, nasty, filthy affair...” To calm rumors regarding Fanny’s relationship with Joseph, the church quickly adopted a “Chapter of Rules for Marriage among the Saints”, which declared, “Inasmuch as this church of Christ has been reproached with...polygamy; we declare that we believe, that one man should have one wife...” This “Article on Marriage” was canonized and published in the Doctrine & Covenants. In 1852, the doctrine of polygamy was publicly announced, thus ending eighteen years of secret practice. “The Article on Marriage” became obsolete and was later removed." ((Mormon Polygamy: A History pgs 6,10,85, Mormon Enigma: Emma Hale Smith pg 66; In Sacred Loneliness: The Plural Wives of Joseph Smith pgs 28,36)
"Fanny stayed with relatives in nearby Mayfield until about the time Joseph fled Kirtland for Missouri. Benjamin Johnson remembers: “Soon after the Prophet[‘s] flight in the winter of ’37...The Alger Family left for the west and Stop[ped] in Indiana for a time...Soon [Fanny] Married to one of the Citizens of ther & altho she never left the State She did not turn from the Church nor from her friendship for the Prophet while She lived..” Benjamin continued, “And I Can now See that as at Nauvoo – So at Kirtland That the Suspicion or Knowledge of the Prophets Plural Relations was one of the Causes of Apostacy & disruption at Kirtland altho at the time there was little said publickly upon the Subject.” Fanny lived the rest of her life in Indiana with her children and husband, Solomon Custer." ((In Sacred Loneliness: The Plural Wives of Joseph Smith pgs 37,39,41)
Source Material: http://wivesofjosephsmith.org/02-FannyAlger.htm