In his homily on Sunday to mark the 166 years of the sisters being in Monaghan and the closing of their motherhouse, the bishop said they made a huge contribution to Irish society in education,healthcare, and community needs.
At the mass of thanksgiving at St Macartan's Cathedral in Monaghan town, Bishop Duffy told the hundreds gathered that the past 30/40 years have not been easy for religious sisters.
He told the congregation that the press seems to love a negative story rather than focus on the wonderful contribution they have made.
He told the Sisters of St Louis that we know what you have done for us in Monaghan, and we will be forever grateful.
Meanwhile, An exhibition titled 'The Story of the St Louis Sisters in Monaghan' will go on public display at the Monaghan County Museum until the 29th of March.
Monaghan County Council recently acquired the St Louis campus, which includes a number of already vacated buildings and lands.
The local authority's Reimagining Monaghan project has been developed for the town and the St Louis Convent grounds.