MMA isn’t illegal in any U.S. state. New York just did a pro MMA event that was in the news a few months ago. There are 4 states where mixed martial arts is unregulated by a state athletic commission. They are New York, Connecticut, Montana, and Alaska.
MMA first came to the attention of many in North America after the Gracie family decided to showcase its trademark Brazilian jujitsu in the United States in the 1990s. Hélio's son Royce Gracie represented the family in a 1993 tournament in Denver, Colorado, that came to be called UFC 1.