On January 6, 1955, work was begun on a new church and school under the direction of the new pastor, Father Cecil Koop, OF.M. at the current location of 195th Street and 115th Avenue. The plans were for eight classrooms in the new school building. Within two years, seventh and eighth grades were added. During the sixteen years of Father Koop’s pastorate, the parish grew from 50 to 500 families.
In 1964, eight more classrooms and a second floor were added to accommodate the school’s growing enrollment. Both Mokena and the St. Mary Church communities continued to grow. St. Mary School had a waiting list in most grades, which showed the need for another addition.