The former school building on the northside of the Church and is now used as the church hall, also contained the living accomodation for the Mistress and had its own small playground for the pupils. When open, it was one of the two schools operating in Abergavenny for girls and was probably the first to be established in the town. Almost certainly, it was the first purpose built Girls school to be established in town. It was considered more superior to the one located in the basement of the Volunteers Hall in Tudor Street. Both schools were later superceded by Castle Street School which was opened in 1866. Trinity School continued to teach pupils for another 38 years. It closed its doors for the last time in 1898.
When Abergavenny Borough Council petitioned Andrew Carnegie (the American Philanthropist) to provide a library for the town, Mr Carnegie agreed to do so on the proviso that the Corporation made available a suitable site free from all debt. The council agreed to do this and purchased the former playground belonging to Trinity School for the purpose. The library was built on this site in 1905.