Polygamy was always illegal whenever and wherever the Mormons practiced it. It was even illegal in Canada and Mexico as they only recognize marriages that are legal in the person's home country. John Taylor, the third president of the church, claimed that he believed in keeping all the laws of the United States "except one"…the law in relation to polygamy." (Journal of Discourses, Vol. 20, p. 317)
Most of Joseph Smith's polygamous marriages occurred in Illinois in the early 1840s. The Illinois Anti-bigamy Law, enacted February 12th, 1833, clearly stated that polygamy was illegal. It reads:
Sec 121. Bigamy consists in the having of two wives or two husbands at one and the same time, knowing that the former husband or wife is still alive. If any person or persons within this State, being married, or who shall hereafter marry, do at any time marry any person or persons, the former husband or wife being alive, the person so offending shall, on conviction thereof, be punished by a fine, not exceeding one thousand dollars, and imprisoned in the penitentiary, not exceeding two years. It shall not be necessary to prove either of the said marriages by the register or certificate thereof, or other record evidence; but the same may be proved by such evidence as is admissible to prove a marriage in other cases, and when such second marriage shall have taken place without this state, cohabitation in this state after such second marriage shall be deemed the commission of the crime of bigamy, and the trial in such case may take place in the county where such cohabitation shall have occurred.
Mormon polygamy was never legal, at any time—not even in the Utah Territory from 1847 to 1890.
Marriage is a legal contract between one man and one woman. There has never been a law enacted to allow otherwise. All the married Mormons who immigrated to Utah in 1847 had been married under the civil laws of their respective states; each one of those states had laws against bigamy, thus making monogamy the "common law."
The very reason Brigham Young chose to move to Utah, rather than Oregon, California, or Texas, as others suggested, was because Utah was an uninhabited "no man's land". However, the area was legally Mexican territory and polygamy was illegal in Mexico.
In the United States, marriage is a legal contract regulated by the various states. When the Mormons went to Utah in 1847, all married Mormons at that time had been married under laws of the states they had come from. Utah became U.S. territory in 1848 after the Mexican War, and thus all citizens living therein became subject to the common laws of the nation, including marriage laws. (To use an analogy, you get your drivers' license from your state, but it is recognized as being legal in all the states. Marriage licenses are similar.)
Once in Utah, Young attempted to establish the "Territory of Deseret," and operate the area as a theocracy, under the "Law of the Lord," which included plural marriage and blood atonement. However, Congress rejected Young's attempt, and in 1850, the area was officially established as Utah Territory, with territorial overseers appointed from Washington D.C. President Millard Fillmore appointed Young as governor. Thus, polygamy became specifically illegal under U. S. common laws in 1850; but, since polygamy was also illegal under Mexican laws beforehand, there was never a time when polygamy was legal in Utah.
The 1862 federal Morrill Act was not the first law which made bigamy illegal; it was merely the first law which specifically reinforced existing state anti-bigamy laws. It was enacted specifically to close the "loophole" that the Mormons mistakenly believed they were operating under.
Even after the passage of the 1862 Morrill Act, the Mormon Church continued to practice polygamy in violation of the law for another half-century, and repeatedly challenged those laws. So anyone who argues that "The Mormons stopped practicing polygamy when it was made illegal" is either misinformed or misrepresenting the truth.
The final nail in the coffin which demonstrates polygamy's illegality was when Ann Eliza Webb filed for "divorce" from Brigham Young and sued him for alimony in 1877. Young successfully argued that their relationship was "an ecclesiastical affair, not a legal one," and the judge rightly ruled that since there was never any legal marriage, Webb could not file for divorce nor seek alimony.Since Young himself admitted that his own "plural marriages" were not legal marriages, that means that no other Mormon "plural marriage" at any time was a legal marriage either. No legal marriage licenses were ever applied for nor granted, and every single child born of Mormon "plural marriages" was illegitimate - i.e. not born in a legal marriage.
All of the federal laws enacted against Mormon polygamy from 1862 to 1879 merely served to force the Mormons to comply with existing common laws. But the fact that those additional laws were enacted does not mean that Mormon polygamous marriages were ever legal in the first place.
In 1878, the United States Supreme Court upheld the conviction of a Mormon under the federal statute prohibiting bigamy against a challenge that, among other things, the statute infringed on the first amendment right to freedom of religion.
http://www.mormonthink.com/joseph-smith-polygamy.htm
Kolob’s set time is “one thousand years according to the time appointed unto that whereon thou standest” (Abraham 3:4). I take this as a round number. - Gee