If you get married in islamic law but not in the states eyes, and have relations with the one you married is that adultury.
Praise be to Allaah.
If you get married according to the law of Allaah and His Messenger, it does not matter if the whole world of man-made laws disagrees with that. She will be your legitimate wife and you can have relations with her whenever you wish – this is not considered to be haraam or adulterous. How could it be, when you have married her according to the sharee’ah and it has become legitimate for you to have intercourse with her by the word of Allaah! This ruling is also of benefit to anyone who may wish to marry more than one woman in countries where polygyny is forbidden by jaahili man-made law. And Allaah is the Source of strength.