Runcorn, city (1991 pop. 63,995), Halton, W England, on the Mersey River. It is located on the Manchester Ship Canal and is the terminus of the Bridgewater Canal, which is connected to the Mersey by a series of locks. The main industry is the production of chemicals. Shipbuilding and ironworks are also important. Runcorn owes its development chiefly to the construction of the Bridgewater Canal in the 18th cent. It was the site of a castle of Æthelflæd in the 10th cent. Runcorn was one of the new towns designated in the 1960s to accommodate overpopulation in the Liverpool and N Merseyside areas.