From 1667 through 1669 he made a missionary tour of the Western missions. He served as a missionary to the Potawatomi Indians in Wisconsin. The next year he was with the Mesquakie, establishing St. Mark's Mission, and founding the mission of St. James among the Miami and Mascouten Indians, finally returning to Green Bay later that year. He said the first mass in Oconto, Wisconsin. The small village of Allouez, Wisconsin near Green Bay, is named for him, as is a trail on Mackinac Island, in Northern Michigan, the Allouez Trail. In 1671, in Sault Ste. Marie, Michigan, he was a principal speaker at the ceremony which formally declared the North West Territory subject to the King of France. In 1671 he founded the St. Francis Xavier Mission at the last set of rapids on the Fox River before entering the Bay of Green Bay. The site was known as Rapides Des Pères (rapids of the fathers) which became modern day De Pere, Wisconsin.
A good portion of Father Allouez’s written work from the time has been preserved. It provides insight into the missions of the time and provides a record that is extensive and important of the Catholic Church in mid-America. As well, it contains the first documented accounts of the Illinois Indians.
