Runcorn is an industrial town and cargo port in the Borough of Halton, Cheshire, England. Runcorn is on the south bank of the River Merse…Runcorn is an industrial town and cargo port in the Borough of Halton, Cheshire, England. Runcorn is on the south bank of the River Mersey, where the estuary narrows to form the Runcorn Gap. It is 15 miles upstream from the port of Liverpool. The Runcorn built-up area had a population of 61,145 at the 2021 census.