(Church history from official sources):

After God revealed the doctrine of plural marriage to Joseph Smith in 1831 and commanded him to live it, the Prophet, over a period of years, cautiously taught the doctrine to some close associates. Eventually, he and a small number of Church leaders entered into plural marriages in the early years of the Church. Those who practiced plural marriage at that time, both male and female, experienced a significant trial of their faith. The practice was so foreign to them that they needed and received personal inspiration from God to help them obey the commandment.

When the Saints moved west under the direction of Brigham Young, more Latter-day Saints entered into plural marriages.

http://www.lds.org/topics/polygamy-plural-marriage?lang=eng