This extensive collection of chapel records consists of items such as a Chapel Register, 1887 - 1905, an incomplete series of Annual Reports, 1886 - 1984 and a Pew Rent Book, 1894 - 1933. The Membership Books date from 1867 - 1885.
The Accounts include an early Treasurer's Account Book, 1854 - 1865; a bundle of collection books, 1898 - 1930; monthly collection books, as early as 1854 and various other accounts and records of income and expenditure. There are even details of the cost of building the first chapel.
There are minute books, 1854 - 1865, which include details of sermons and preachers and collections, with a reference to the opening of the chapel. Numerous other minute books belong to various Twrgwyn committees and officials e.g. Twrgwyn Chapel Choir, 1922-1929.
The Sunday School records include accounts, membership books, and minute books.
Other miscellaneous material are lists of members and membership ticket books, 1955 - 1993; bundles of correspondence and papers regarding the maintenance of the chapel, 1982 - 1995; general correspondence; a note book with lists of preachers, ca 1870 - 1890; 3 membership tickets, 1981; and a programme of plays held at Twrgwyn in 1984.
The collection also contains a Minute Book of the Bangor Free Church Council, 1910-1920; notes made on sermons preached at Twrgwyn and Tabernacl Chapels, Bangor, 1862; Treasurer's Book of the North Wales Calvinistic Methodist Ministers' Fund, 1879 - 1904 and accounts of the Caernarfon and Bangor Cymdeithasfa, 1905 - 1913.