I heard of Teimanim who have more than one. Don’t know if they married back in Yemen to both, before moving out of the country. I also heard some Sefardim came to Eretz Yisroel with more than one, when they emigrated in the early days of the State.
Some Mormons do it. The way they keep it legal is by not having a civil marriage with more than one. It is only illegal if there is more than one civil marriage in the U.S. Otherwise its just as legal as every other goy who has a bunch of girlfriends or lives unmarried with more than one woman in his house and whatever other crazy lifestyles the goyim do. Some of it may be nuts, but the law doesn’t bother anyone with an alternative lifestyle these days.