For well over a thousand years November 1st has been remembered by Catholics as All Saints day. The praying for the souls of those who should have been made saints, but weren't, and those who were, starts after Vespers on 31st October.
Saints are 'hallowed', hence the term Hallow, and the term 'Halloween' for the evening before all Hallows (Saints) day....and the term 'All Hallows Day' for November 1st.
The Irish remained Catholics long after England became Protestant, and probably merged some of their Pagan customs with others. Although what part of Ireland that would have happened in is anyone's guess.
Love bears all things,believes all things,hopes all things,endures all things. Love never ends. 1 Corinthians: 13