Inspiring answers, thank you, which have somehow sparked the flow of further information. I had a search with Montgomoryshire in mind & came up with these dates & places:
County ; Montgomeryshire
district ; Llanfyllin/Llansantffraid (Llansanffraid), Llansantffraid-ym-Mechain/Llansantffraid Pool
Place ; Glyn Ceirog
Chapel ; Seion Welsh Baptist Chapel / Baptist / 1762, rebuilt 1875 (actually 1874 according to the date stone)
Llansantffraid-ym-Mechain/Llansantffraid Pool
Place ; Glyn Ceirog /Salem Welsh Baptist Chapel / Baptist / 1832
Llansantffraid-ym-Mechain/Llansantffraid Pool
Place ; Glyn Ceirog
Chapel ; Soar Welsh Calvinistic Methodist Chapel / Calvinistic Methodist / 1875
Llansantffraid-ym-Mechain/Llansantffraid Pool
Place ; Nantry
Chapel ; Capel Nantyr Welsh Baptist Chapel / Baptist / 1905 / Late 20th century
Llansantffraid-ym-Mechain/Llansantffraid Pool
Place ; Pandy
Chapel ; Penuel English Baptist Chapel; Capel Pandy / Baptist / 1894
Llanfyllin
Place ; Llangadwaladr
Chapel ; Tregeiriog Chapel / Calvinistic Methodist / 1804
The building date stone reads 1878 so perhaps this was rebuilt? They wouldn't refer to Calvenist Methodist as Baptists on the registers would they? Wouldn't think so but you can tell I'm into a new area of research here This information clearly gives 2 Baptist churches standing in the year 1849, that info found in A Topographical Dictionary of Wales, Author; Samuel Lewis 4th Edition, 1849, Glyn Ceiriog. There's the Salem Chapel 1832 & as mentioned in morganllan's earlier post, the Seion Chapel 1762, rebuilt 1875. As my John had his birth registered in 1824 I'm going to assume with caution that both entries including his 1848 baptism took place at the earlier Seion Chapel. The birth entry has good details of parents, date & place of birth but the baptism is a simple list of names in that year, with the occupation noted next to the name in some case. Our John Isaac has 'Gof', nice word that, I wonder if it has 'owt to do with hammer.
Thanks for the information so far, a picture slowly builds & a reminder to bring Montgomoryshire into the equation when searching around Glyn Ceiriog during certain time frames.
Richard