Wallasey is on the Wirral Peninsula - a piece of land surrounded by water on three sides. To the west is the River Mersey, to the east is the River Dee and to the north is part of the Irish Sea known as Liverpool Bay. On the southern side it is the Cheshire Plain.

Wallasey's name is derived from the Gaelic "Wealas Eye", which roughly translated means Welshman's or Stranger's Island. Wallasey was an island at high tide, being cut-off from the surrounding land by Wallasey Pool (now Wallasey and Birkenhead Docks), and Moreton Marshes which were drained in the 1800's with the building of a sea wall along the Liverpool Bay coastline. Today it is still impossible to enter or leave Wallasey without crossing water of some description.

Wallasey may be one of the longest established dwelling places on the Wirral. When excavations on Saint Hilary's Brow (the highest point in the town) were taking place in the last century, artifacts dating from the Stone and Iron Ages were discovered.