During this period of fear and confusion in the aftermath of the earthquake, the people of the diocese received good news. Joseph M. Gilmore, Chancellor of the diocese, had been named its fifth bishop. Although born in New York, Bishop Gilmore had been raised in Anaconda, and had served as a priest in the diocese prior to his election. His 26-year episcopacy was one of growth for the diocese. In addition to the material development, programs were developed to foster vocations, help resettle refugees, retrain unskilled workers, aid in adoptions, promote the lay apostolate, as well as care for the spiritual welfare of the flock.

In 1941, the diocese celebrated the 100th anniversary of the arrival of Catholicism in Montana. It was in 1841, when Father DeSmet founded St. Mary's Mission in the Bitterroot Valley, the first Catholic Church in Montana. The Diamond Jubilee of the diocese and the Golden Jubilee of the Cathedral were celebrated April 16, 1959. Bishop Gilmore died very unexpectedly in San Francisco on April 2, 1962.