Final answer:
Spanish missionaries and colonists were the first migrants to bring Catholicism to what is now the United States, especially in the Southwest and Florida.
Step-by-step explanation:
The group of migrants who first brought Catholicism to what is now the United States were Spanish missionaries and colonists, particularly in the regions that would become the American Southwest, Florida, and other parts of the New World conquered by Spain. These Spanish Catholics converted many of the indigenous people, and their influence is a significant part of the history of Catholicism in the country. The Jesuits from France were also instrumental in spreading Catholicism, particularly in what is now Canada and stretching down into the northern United States, working mainly with Native American populations.