 The commote of Glynrhondda was coterminous with the earlier parish of Ystradyfodwg , but little is known of the Celtic saint Tyfodwg , or Dyfodwg after whom the parish is named . Saint Tyfodwg is thought to have existed around 600 AD , and although the parish bears his name there are now no religious monuments or places of worship named after him within the Rhondda boundaries . There are two churches in South Wales outside the area named after the saint ; Y Tre Sant in Llantrisant and Saint Tyfodwg ’ s in Ogmore Vale . 
