Pierre De Smet was born in Termonde, Belgium on January 31, 1801. He attended a seminary school where he met Father Charles Nerinckx - a missionary from Kentucky. During his visit he told stories of his travels and about the opportunities available to minister to the tribes in America. This is when De Smet decided to accompany Father Nerinckx on a mission trip.
In 1839. De Smet met an Iroquois Indian by the name of Ignace Los Angeles Mousse. He had married into the Flathead tribe, and told the Flatheads about the Catholic priests in the east. The Flatheads decided they wanted these men to come and minister to their tribe. When De Smet met Ignace, he decided to go west with his mission right away. In July 1840, he journeyed to the Flathead camp in the Bitterroot Valley. Arriving at their village, he realized that the tribe had already built him a tent. In addition, the whole tribe of 1,600 people came out to give him a warm welcome.
De Smet was uplifted by the tribe's welcoming gestures and began to make plans for building a permanent mission on the site. On August 20, 1840 Pierre traveled to St. Louis to obtain money and men to build the mission. On April 24, 1841 De Smet, along with two priests and three lay brothers, departed from St. Louis to return to the Flatheads, where he remained for several years.