The collection consists of transcripts of the parish registers of Bryncroes, 1730-1962; Penllech, 1785-1957; Llangwnnadl, 1781-1966; Llanfaelrhys, 1812-1951; Rhiw, 1845-1921; Aberdaron, 1814-1944; Llanbedrog, Tudweiliog, 1766-1953 and Pen-y-graig, 1813-1937. Amongst these are copies of Vestry Accounts and some epitaphs collected from various churchyards.
There are notes relating to the families of Llangwnnadl and surrounding parishes as well as family pedigrees.
The shipping section consists of a cargo book, 1910-1914, belonging to the ketch Colonel Gamble and an account book, 1915-1917, of the ketch, Tryfan. There are also notes and poems regarding various shipwrecks off the coast of the Lleyn peninsula.
The miscellaneous items include a collection of rare songs belonging geographically to the Lleyn area; a school exercise book, 1793; a Highway Rate Book, 1884-1889 and Poor Law Rate Book, 1923-1924 for the parish of Llangwnnadl and the account book of William Owen Roberts himself, 1910-1922.There are transcripts of articles, notes and essays on local history and Calvinist Methodism in Lleyn.