In 1870-72, John Marius Wilson's Imperial Gazetteer of England and Wales described Eglwys Bach like this:
EGLWYS-FACH, a village in the district of Llanrwst and county of Denbigh; and a parish, all in the same district, but partly in the county of Carnarvon. The village stands on an affluent of the river Conway, about a mile E of the Conway and Llanrwst railway, not far from Tal-y-Cafn r. station, and 6 miles N of Llanrwst; and has a post office‡ under Conway, and fairs on 24 Feb., 11 May, 24 Aug., and 24 Nov. ...
The parish contains the townships of Bodnod, Cefn-y-Coed, Esgorebrill, and Pennant in Denbigh, and the township of Maenan in Carnarvon. Acres of the Denbigh portion, 7, 838. Real property, £5, 270. Pop., 1, 157. Houses, 257. Acres of the Carnarvon portion, 2, 902. Real property, £1, 845. Pop., 373. Houses, 80. The property is divided. Bodnod is the seat of the Hanmers; and Maenan, on the site of an old abbey, is the seat of the Lenthals. Much of the surface is hilly. The living is a vicarage in the diocese of St. Asaph. Value, £220.* Patron, the Bishop of Llandaff. The church is fair. There are two chapels for Calvinistic Methodists. An endowed school has £25; and other charities £10.
GB Historical GIS / University of Portsmouth, History of Eglwys Bach, in Conwy and Denbighshire | Map and description, A Vision of Britain through Time.
Date accessed: 24th March 2017
Click here for more detailed advice on finding places within A Vision of Britain through Time , and maybe some references to other places called " Eglwys Bach ".