FairMormon is a non-profit organization dedicated to providing well-documented answers to criticisms of the doctrine, practice, and history of The Church of Jesus Christ of Latter-day Saints.
Question: Was polygamy illegal?
Question: Was polygamy illegal?
Contrary to popular belief, the plural marriages in Illinois were not illegal under the adultery statutes of the day
- Prior to the first anti-polygamy statute for the U.S. Territories (the Morril Act of 1862), no law forbade polygamy in the Great Basin region.
- Polygamy was certainly declared illegal during the Utah-era anti-polygamy crusade (i.e., from 1862 onward). The Saints refused to comply with the law during that period because they believed:
- a) that the law was unconstitutional and violated their right of religious worship; and
- b) that God had commanded them to practice plural marriage despite the potential legal penalties.
The Church believes in honoring and sustaining the law, but it does not believe that members must surrender their religious beliefs or conscience to the state
Not surprisingly, the question comes down to whether Joseph was a Prophet and whether God commanded his actions.
Just because some members have come up with uninformed opinions about plural marriage, is this the Church's fault? The Church doesn't include any of these claims in its manuals.
The practice of polygamy during periods when it was illegal is a clear case of civil disobedience
This is hardly new information, and Church members and their critics knew it. Modern members of the Church generally miss the significance of this fact, however: the practice of polygamy during periods when it was illegal is a clear case of civil disobedience.
The decision to defy the [anti-polygamy laws] was a painful exception to an otherwise firm commitment to the rule of law and order. Significantly, however, in choosing to defy the law, the Latter-day Saints were actually following in an American tradition of civil disobedience. On various previous occasions, including the years before the Revolutionary War, Americans had found certain laws offensive to their fundamental values and had decided openly to violate them.…Even though declared constitutional, the law was still repugnant to all [the Saints’] values, and they were willing to face harassment, exile, or imprisonment rather than bow to its demands. 
Elder James E. Talmage taught that members should obey the law, unless God commanded an exception:
A question has many times been asked of the Church and of its individual members, to this effect: In the case of a conflict between the requirements made by the revealed word of God, and those imposed by the secular law, which of these authorities would the members of the Church be bound to obey?…Pending the overruling by Providence in favor of religious liberty, it is the duty of the saints to submit themselves to the laws of their country. 
- James B. Allen and Glen M. Leonard, Story of the Latter-day Saints, 2nd edition revised and enlarged, (Salt Lake City: Deseret Book Company, 1992), 401. ISBN 087579565X. GospeLink (requires subscrip.)
- James E. Talmage, The Articles of Faith (Salt Lake City, Utah: Deseret Book Company, 1981),382–383.