The Church of Jesus Christ of Latter-Day Saints has, but they're a split-off group of the main Mormon church, however more popular than the main church that the CoJCoLDS (heh...) has grown. There are also a great deal of churches split off from the big one with the long name, so it's hard to track how many Mormon polygamists there are besides looking into the main church.

In any case, the USA has plenty of them in the Midwest, often fewer than investigations reveal because of the sensitive, illegal nature of the problem, which tends to form closed communities. Canada's largest Mormon polygamist settlement numbers at around 3000 people, somewhere in BC.