When was Saint Dymphna canonized?

Saint Dymphna, Patron Saint of those who suffer from mental illness, lived and died around the 7th century, long before the formal act of canonisation was instituted and therefore was never canonised by the Pope. Until Canonisation was reserved to the Pope it was customary for local areas to honour members of the community for their sanctity and these people are called Saint with equal regard as those who have been formally canonised.