St. Joseph Co-Cathedral is a Catholic cathedral located in Thibodaux, Louisiana, United States. Along with the Cathedral of St. Francis de Sales in Houma it is the seat of the Diocese of Houma-Thibodaux. It is also the oldest parish in the diocese. The church building and rectory are listed on the National Register of Historic Places as Saint Joseph's Co-Cathedral and Rectory.HistorySt. Joseph Parish first began to organize in 1813 and was founded as a mission to Assumption Church in Plattenville in 1817. Two years later a small wooden church building was constructed near the current church cemetery. The Rev. Antoine Potini was assigned as St. Joseph's first pastor. It is the oldest Catholic parish in the diocese and many of the other churches were founded from it and served by its priest. The Rev. Charles Menard had a brick church built in 1849 and it was destroyed by a fire in 1916. The relics of Saint Valerie survived the fire and are in the current church in a glass sarcophagus. The present church was begun in 1920 during the pastorate of Msgr. Alexander Barbier. It was completed three years later in the Renaissance Revival style. The first Mass was celebrated on January 25, 1923. The ornamental marble and plaster work was added in 1931 and the final paint scheme was done in 1954.