Details of the growth and development of Fochriw, Pentwyn and Penybank are based on the 1851, 1861, 1871, 1881, 1891 and 1901 census returns and various Ordnance Survey maps.
Both the Tithe Map and Census of 1851 depicts only 2 buildings within the curtilage of what is now Fochriw, these being Llwyn Iago Farm and the Rising Sun Inn which is called the Cae Glas Inn on the census and was at numbers 3, 4 & 5 Williams Row.
Fochriw is spelled Fochrhiw, whilst Pontlottyn, which is located 1 mile to the east in the Rhymney valley, is represented by eight detached dwellings and four short terraces of houses. It is interesting to note that it is identified as Lottyn with the bridge over the river Rhymney as Pont Lottyn.
Pentwyn is shown as being only Ffynnonau Duon farm, whilst Penybanc consists of a list of locations which are mainly farms, these being, Darran Ddu (Cilhaul?), Cwm Llwydrew, Penybank farm, Glan Bargoed, Tyla Du, Brithdir Usha which is located on the eastern side of the valley adjacent to Penybanc and Brithdir Isa, which is also on the eastern side of the valley above what was the site of Ogilvie Colliery. The latter two being corruptions of Uchaf (higher) and Isaf (lower)respectively.