"YSTRAD MYNACH is an ecclesiastical parish, formed in 1890 from parts of Gellygaer and Llanfabon, by Order in Council. It has a station on the Great Western Railway, and is 6 miles north-east of Pontypridd and 18 north-east from Cardiff, in the Caerphilly division of the county of Glamorgan, hundred, union and county court district of Pontypridd, petty sessional division and rural deanery of Caerphilly, and archdeaconry and diocese of Llandaff. The church of Holy Trinity, erected about 1857, is a building of stone in the Gothic style, ... there are 140 sittings. The register dates from the year 1890. The living is a vicarage, net yearly value £250, with residence, in the gift of the Bishop of Llandaff and the Board of Patronage, ... The population in 1911 was 2,081. ... " [From Kelly's South Wales Directory 1923 (ArchiveCDBooks) - transcribed by Gareth Hicks]
Williams, E. H., and Sons, drapers, London House, Ystrad Mynach records "Business records of E. H. Williams and Sons, including: diaries, 1904-1933; bank books, 1914-1928; purchase book, 1914-1917; cash books, 1917-1931; accounts of goods returned, 1914-1917; credit book, 1923-1936; staff attendance book, 1922-1935; catalogues and brochures, [1920s]-[1940s]; and photograph of London House, [c. 1930]."
The church is dedicated to Holy Trinity, is in the Benefice of Ystrad Mynach with Llanbradach, and the diocese of Llandaff. Details of the present incumbent of this benefice can be found at the Church in Wales website. The church can be located at grid reference ST144942.
Thomas family, of Llanbradach and Ystrad Mynach estates, records "Deeds and documents relating to the Llanbradach, Ystrad Mynach and Tredomen estates in Glamorgan, [c. 1528]-[c. 1944], and to a lesser extent, Monmouthshire, 1701-1942; and to the Pencerrig estate in Breconshire, 1680-1933, and Radnorshire, 1574-1923; ..............................."
You can see maps centred on OS grid reference ST145943 (Lat/Lon: 51.640934, -3.237002), Ystrad Mynach which are provided by: