The collection consists of personal and family papers such as copies of birth certificates; genealogical material; diaries, 1899 -1957; Sabbath diaries, 1907 - 1958; photographs and a biography. There are also collections of poetry by Rev. John Henry Williams, some of which were composed for Eisteddfod competitions, 1894 - 1970. Essays, addresses, lectures and a play are also amongst his own compositions.
The letters are from various correspondents to Canwy, 1899 -1968, including a group from T. Gwyn Jones, Aberystwyth, 1918 - 1924 on subjects such as the war and Welsh grammar.
The miscellaneous material includes a summary of the history of Hermon chapel, Llanfachreth, Merionethshire; a minute book of brethren meetings at Mynydd Isaf chapel, near Mold, 1914 - 1915; a list of members married and buried by Canwy from 1913 - 1961 and a contribution book of Y Graig chapel, Penrhosgarnedd, Bangor, 1924 - 1942. Also, newspaper cuttings, 1899 - 1958 which consist mostly of his poetry.