town and port in Allerdale district, administrative county of Cumbria, historic county of Cumberland, northwestern England, on the Solway Firth where it joins the Irish Sea. The town lies at the mouth of the River Derwent. During the 19th century it grew up around a medieval castle as a coal-mining and iron and steel centre. Coal mining has ceased, but steel production and other manufactures continue. The port is centred on the Prince of Wales Dock, opened in 1927. Pop. (2001) 21,514.