 The Ely's numerous sources lie in the mountains to the south of Tonypandy, near the town of Tonyrefail, rising in the eastern slopes of Mynydd Penygraig (Penygraig) and Mynydd y Gilfach (Penrhiwfer) and the western slopes of Mynydd Dinas (Williamstown), whose eastern slopes feed the Rhondda by Porth.The source of the Ogwr Fach lies just to the west.After flowing through Tonyrefail and through the grounds of the Royal Glamorgan Hospital at Ynysmaerdy, it follows the A4119 road through the valley pass formed between Mynydd Garthmaelwg (Llantrisant Forest), to the west and Llantrisant, to the east.