There are remote towns where polygamy is rampant among the Mormons who reside in them. How do they get away with it? Because the mayors, councilmen, police force and other powerful officials who run the towns are either polygamists or sympathetic to the practice. Really, Utah's governments are basically over run by politicians who are Mormon.
Let's be clear about this.... yes, the Mormons discontinued polygamy so that the state of utah could join the union, but it too was the case that that the federal govenment impounded their money and imprisioned some of their people. In the 1800's, as weird as it seems, there was NO civil law against polygamy, it was a "moral" law of the people. It became a federal law after the mormons were practicing it.
Secondly, in today's society you're talking about TWO distinct groups. The mainstream Mormons, (over 12 million members) and the comparatively small wacko polygamists, which some people use the phrase fundementalists.... they're the polygamist groups you see that are being reported in television programs. Yes, those small fundamentalist towns do have the politicians in their back pocket, because they too are polygamists...but we're talking VERY SMALL towns. The civil authorities in Utah (mostly mainstream Mormon) are going after the polygamists, and the mainstream Mormon church excommunicates anyone involved in polygamy. I think the FEDS should go into Southern Utah (where the fundies are) and clear them all out, but they tried that in the early 1950's and it backfired on them.... there was a huge outcry from Americans about the way the Feds treated them, even though they didn't like the practice.