Since the dumass who actually thinks they are Mormon because they were converted recently won't, I was raised at the time BEFORE they stopped the practice in the LDS church *pauses for drug related jokes* and here is some links:
Mormon polygamy <- Straight from the mouth of the church itself.
THE POLYGAMY DILEMMA AND THE BOOK OF MORMON <- Though not from the church, the Witnesses and Mormons are very much alike in many aspects save this one so they argue it out all the time.
The church disavowed it earlier than the practice itself was stopped. Even in Utah the practice still persists on a smaller scale. It was taken as a way to fulfill one commandment "be fruitful and multiply" found in the BofM. Officially the practice did not stop until the early 80's late 70's, at which time the polygamist marriages were finally broken up.
So, stupid LieSpeaker, try again.