The Cathedral Museum, located inside the Cathedral Center, features memorabilia of the early bishops of the diocese and pastors of the Cathedral, historical documents, liturgical vestments, and vessels of the pre-Vatican II era. The museum also commemorates the persons and events that contributed to the history of St. John Cathedral Parish which spans 185 years. Included in the exhibit are the official diocesan and papal documents which established both the parish in 1821 and the diocese in 1918. In addition to photographs and books of priests who have served in the parish are memorabilia of four notable persons who are buried in the church or its cemetery: Bishop Jeanmard, first bishop of Lafayette; Bishop Schexnayder, second bishop of Lafayette; Bishop Gerald Frey, third bishop of Lafayette; and Ambassador Jefferson Caffery, ambassador to France.