This collection consists of material accumulated by the Elias family of Llanrwst, Denbighshire and Penmaenmawr, Caernarfonshire (now in Gwynedd) in particular by Thomas Elias, genealogist and antiquary and his great grandfather, the poet and genealogist William Elias.
Material mainly relates to the genealogy of certain well-known families in north Wales and the archaeology of the area. It includes a bound volume on Welsh genealogies from the collection by Owen Gruffydd of Llanystumdwy, poet and antiquary, which was inscribed and presented to his pupil William Elias. Also includes a volume containing pedigrees of well-known Welsh families and details on Caernarfon sheriffs compiled by Thomas Elias. Also includes Elias family pedigrees and miscellaneous deeds and other documents accumulated by Thomas Elias.