Irby lies on the western side of the northern part of the Wirral Peninsula, from the Irish Sea at Hoylake, from the Dee Estuary and about from the River Mersey at Tranmere. Irby sits on the eastern side of Thurstaston Hill, at the western side of a wide and shallow glacial U-shaped valley, formed during the Quaternary Ice Age. The underlying bedrock is Triassic bunter sandstone of the Helsby Sandstone Formation, and Triassic siltstone of the Tarporley Siltstone Formation. This is overlain with boulder clay from the Quaternary Ice Age, similar to the nearby Dee Cliffs, and clay soil. The bedrock is not usually visible, as it is at the summit of Thurstaston Hill.