The roughly rectangular peninsula is about 15 miles (24 km) long and 7 miles (11 km) wide. Historically, Wirral was wholly within Cheshire; in the Domesday Book, its border with the rest of the county was placed at "two arrow falls from Chester city walls." However, since the passing of the Local Government Act 1972, only the southern third has been in Cheshire, with the rest in the Metropolitan Borough of Wirral in the modern county of Merseyside.
Wirral contains both affluent and deprived areas, the former largely in the west, south and north coast of the peninsula, and the latter concentrated in the east, around the built-up district of Birkenhead.
The name Wirral literally means "myrtle corner", from the Old English wir, a myrtle tree, and heal, an angle, corner or slope. It is supposed that the land was once overgrown with bog myrtle, a plant no longer found in the area, but plentiful around Formby, to which Wirral would once have had a similar habitat. The name was given to the Hundred of Wirral (or Wilaveston) around the 8th century.
The earliest evidence of human occupation of Wirral dates from the Mesolithic period, around 7000 BC. Excavations at Greasby have uncovered flint tools, signs of stake holes and a hearth used by a hunter-gatherer community. Other evidence from about the same period has been found at Irby, Hoylake and New Brighton. Later Neolithic stone axes and pottery have been found in Oxton, Neston, and Meols. At Meols and New Brighton there is evidence of continuing occupation through to the Bronze Age, around 1000 BC, and funerary urns of the period have been found at West Kirby and Hilbre.
Before the time of the Romans, Wirral was inhabited by a Celtic tribe, the Cornovii. Artefacts discovered in Meols suggest it was an important port from at least 500 BC. Traders came from Gaul and the Mediterranean localities to seek minerals from North Wales and Cheshire. There are remains of a small Iron Age fort at Burton, for which the town was named (burh tún being Old English for "fort town").