Treforest on Wikipedia.
 

All Nations Church, previously Saron Calvinistic Methodist Church. Another view. © David Gallimore.

Castle Square U.R.C. © Gervase N. E.  Charmley.

Calvary English Baptist Church dating from 1851. Gervase advises that this is the oldest English Baptist Church between Cardiff and Merthyr. © Gervase N. E.  Charmley.

Libanus Chapel (Baptist). © Gervase N. E.  Charmley.

Parc Presbyterian Church, on Princess Street, dating from 1909. © Gervase N. E.  Charmley.

St. Dyfrig (R.C., opened 1927). © Gervase N. E.  Charmley.

Treforest Gospel Hall, aka The Church on the Broadway. © Gervase N. E. Charmley.

Wesleyan Methodist Church. © Gervase N. E.  Charmley.

A former church on Bridge Street. © Gervase N. E.  Charmley. Janet Gimber has advised that this building appears on old maps as St. Dubritius's R.C. Chapel (alternatively, St. Dyfrig's), when the street-name was Wood Street. By 1927 its licence to hold weddings had been revoked, so presumably was no longer in use. On a map of 1943, it shows as "Hall" and in 1960 as "Boys Club". Presumably the closure of this chapel was followed at some point by the opening of St. Dyfrig (above). My appreciation to Jim O'Brien, who has advised that a lease was taken out in 1849 on two properties in Wood Street, 72 and 73. Whether there were any pre-existing buildings here is unclear, but if there were, they were demolished to allow the building of "Old St. Dubricius and Catholic Hall". It presumably ceased as a church around 1927 when the new church was opened.