The River Ray rises around 1500m north of Quainton, Buckinghamshire [Map] from where it flows broadly west past Grendon Underwood, Buckinghamshire [Map], Blackthorn, Buckinghamshire [Map], Lower Arncott, Oxfordshire [Map], Merton, Oxfordshire [Map], Oddington, Oxfordshire [Map] to Islip, Oxfordshire [Map] where it joins the River Cherwell.