At this period, he revived the Catholic faith among parishioners, who had been made indifferent by the proximity of the Protestant cantons of Switzerland.

[1] Crétin was one of the few who volunteered and on August 16, 1838, he secretly left his parish, embarked at Le Havre on board the Lyons with Bishop Loras, and landed in New York on October 12 of the same year.

The winter of 1838-39 was spent in St. Louis, Missouri, and on his arrival in Dubuque, April 18, 1839, he was immediately appointed vicar-general of the new diocese.

For over eleven years, he exercised his priestly ministry in these new regions, dividing his time between Dubuque, Prairie du Chien, Wisconsin, and the Winnebago Indians in the neighborhood of Fort Atkinson, in Winneshiek County, Iowa.

That evening he made his first appearance in the log chapel of St. Paul, his first cathedral, and gave his first episcopal blessing to his flock.

He also planned the erection of a seminary, and always eagerly fostered vocations for the priesthood, keeping at his residence seminarians in their last period of preparation.

With an eye to the future he endeavored to provide for the growth of his diocese by bringing Catholic immigrants from European countries to the fertile plains of Minnesota.