Mormons stopped practicing polygamy in 1890.
Many Mormons entered into polygamous marriages after 1890. Over 200 polygamous marriages were performed between 1890 and 1904.
note though all Christian religions claim to believe in a book, the Bible, that has people who practiced polygamy blessed by God. It's pretty hypocritical for any one who believes in the Bible to be against polygamy when the God that book is about blessed the practice.