 During the early to mid @-@ 19th century the Rhondda Valleys were inhabited by small farming settlements . In 1841 the parish of Ystradyfodwg , which would later constitute most of the Rhondda Borough , was recorded as having a population of less than a thousand inhabitants . With the discovery of massive deposits of high quality , accessible coal during the mid @-@ 19th century the Rhondda Valleys experienced a large influx of financial immigrants . The first immigrants came to the lower Rhondda villages of Dinas , <unk> and Cymmer . Special sinkers came from <unk> , while the first miners were from Penderyn , <unk> and the neighbouring areas of Llantrisant and <unk> . The 1851 Census lists apprenticed paupers from Temple Cloud in Somerset , some of the earliest English immigrants . From a mere 951 in 1851 , the population of Ystradyfodwg parish grew to 16 @,@ 914 in 1871 and by 1901 the Rhondda Urban District had a population of 113 @,@ 735 . As more and more coal mines were sunk the population grew to fill the jobs needed to extract the coal . In the 1860s and 1870s the majority came from the neighbouring Welsh counties , but with the improving rail transportation and cheaper transport immigrants came from further afield . The 1890s recorded workers from the South West , places such as Gloucester and Devon , by the 1900s people came from North Wales , the lead mining area of Anglesey and the depressed slate @-@ quarrying villages of Bethesda , Ffestiniog and Dinorwig . Although there are records of Scottish workers , mainly centered on Archibald Hood 's <unk> mines , there were only small numbers of Irish , less than 1 @,@ 000 by 1911 . The low immigration levels of Irish workers is often blamed on the forcible ejection of the Irish who lived in Treherbert during three days of rioting in 1857 . The population of the valleys peaked in 1924 at over 167 @,@ 900 inhabitants . 
