You missed something. I think that this says it best:
Throughout the latter half of the nineteenth century, the Church was well-known for its polygamous practices. Despite increasing legal pressure, the members continued their practice of civil disobedience. The announcement of the Manifesto of 1890 introduced a new set of problems. As Elder Dallin H. Oaks noted:
It is clear from the record of history that Joseph Smith introduced the doctrine and practice of polygamy to a select few in the 1830s and 1840s, but it was not announced publicly by the church until the revelation was read aloud at a Church conference in Salt Lake City in 1852. It is also clear that during the federal prosecutions of the 1880s, numerous Church leaders and faithful members were pursued, arrested, prosecuted, and jailed for violations of various laws forbidding polygamy or cohabitation. Some wives were even sent to prison for refusing to testify against their husbands, my grandfather’s oldest sister being one of them.
It is also clear that polygamy did not end suddenly with the 1890 Manifesto. Polygamous relationships sealed before that revelation was announced continued for a generation. The performance of polygamous marriages also continued for a time outside the United States, where the application of the Manifesto was uncertain for a season. It appears that polygamous marriages also continued for about a decade in some other areas among leaders and members who took license for the ambiguities and pressures created by this high-level collision between resented laws and reverenced doctrines.8
fairlds.org/Misc/Polygamy_Prophets_and_Prevarication.html
The above site gives a very comprehensive overview of mormon polygamy.