St. Mel's Museum is located at St Mel's Cathedral , Dublin Street in Longford , Co. Longford.

On Christmas Day 2009, a fire at St. Mel's Cathedral destroyed the interior of the church along with most of its furnishings and fittings. The Diocesan Musuem at the back of the cathedral and its contents also suffered serious damage. The collection included almost 500 items and ranked among the finest ecclesiastical museums in the country. It contained a varied collection of ecclesiastical material as well as objects of archaeological, historical and ethnographical interest. Chief amongst these objects was the 9th century Crozier of St Mel, patron of the diocese, which was found at Ardagh, Co. Longford in the 19th century, the Shrine of St Caillinn of Fenagh, Co Leitrim - a book shrine dated to 1536 and associated with Brian O'Rourke, Lord of Breifne and the 12th century Clog na Rígh - bell of the kings - also associated with St Caillinn.