Books by R.S. Van Wagoner ₃ and Todd Compton ₄ seem to have conclusively dispelled these beliefs as false.

Origins of Mormon polygyny:

Joseph Smith, was the founder of the Church of Christ in 1830. This church eventually split to become the almost 100 denominations and sects forming today's LDS Restorationist movement. Smith first secretly promoted the concept of polygyny during the 1830s. This type of marital structure involves one man married to multiple wives. The practice has been variously called the Law of Abraham, the Patriarchal Order of Marriage, Celestial Plural Marriage, or the Law of the Priesthood. Associated with these was the Law of Sarah. More details.

Joseph Smith himself assigned women to some of the Mormon men. He married dozens of women himself. Mormon writer Todd Compton wrote:

"I have identified thirty-three well-documented wives of Joseph Smith, which some may regard as an overly conservative numbering ...Historians Fawn Brodie, D. Michael Quinn, and George D. Smith list forty-eight, forty-six, and forty-three, respectively. Yet in problematic areas it may be advisable to err on the side of caution." ₄

His first wife was Emma. He married his second wife Fannie Alger in 1833 when she was 17 years of age. He apparently secretly married Emma's counselor and her secretary in the Nauvoo Relief Society.  Emma was president of the group. "This was apparently done without Emma's knowledge or consent." It is reported that one wife was only fourteen years of age at the time that she married Joseph. _1,2

When the Mormons were centered in Nauvoo, IL (previously called Commerce, IL.) during 1844, a group led by the First Presidency counselor, William Law, split from the teachings of Joseph Smith.  They printed the first of a series of publications in the local newspaper, "The Nauvoo Expositor." It exposed some of the secret practices of church members, including plural marriage. Before subsequent editions could be printed, allegedly "Smith and the city council had the press destroyed." ₁ Smith and his brother Hyrum were arrested for the alleged crime. A mob later broke into the jail and assassinated both of them.

Brigham Young's promotion of polygyny:

It was not until eight years after Joseph Smith's death, on 1852-AUG-29, that the LDS Church publicly acknowledged the practice of polygyny. ₁"It was read in the conference held in Great Salt Lake City, and Apostle Orson Pratt delivered the first public discourse on that principle." ₅

Brigham Young replaced Joseph Smith as head of the LDS Church after Smith's assassination. He continued to promote the practice of polygyny. He had 55 wives of his own and fathered 56 children during his lifetime. Some quotes from Mormon sources: