Rees, Thomas & John Thomas.Hanes Eglwysi Annibynnol Cymru(History of the Welsh Independent Churches), 4 volumes (published 1871+). Here is the entry from this book for Dwygyfylchi chapel (in Welsh ) - with translation by Eleri Rowlands (April 2012)
Church and chapel data from The Religious census of 1851 : A Calendar of the returns relating to Wales, Vol 11, North Wales. Ed. by Ieuan Gwynedd Jones, UWP,1981. The names given towards the end of each entry are those of the informants.
Dwygyfylchi Parish; Statistics; Area 5794 acres; Population 467 males, 459 females, total 926
The return in respect of the parish church is missing
A separate enquiry form from the Superintendant Registrar dated Sept 1852 refers to a congregation of 80 and scholars 40
Penmaenmawr Urban District Council records (additional deposit) - details of extant records on Archives Network Wales "Includes; Minutes, accounts and letter books, Dwygyfylchi Local Board, 1880-1890...."