Calderdale is a metropolitan borough of West Yorkshire, England, whose population in 2020 was 211,439. It takes its name from the River Calder, and dale, a word for valley. The name Calderdale usually refers to the borough through which the upper river flows, while the actual landform is known as the Calder Valley. Several small valleys contain tributaries of the River Calder. Calderdale covers part of the South Pennines, and the Calder Valley is the southernmost of the Yorkshire Dales, though it is not part of the Yorkshire Dales National Park. The borough was formed in 1974 by the merger of six local government districts, from east to west Brighouse, Elland, Halifax, Sowerby Bridge, Hebden Bridge and Todmorden. Mytholmroyd, together with Hebden Bridge, forms Hebden Royd. Halifax is the commercial, cultural and administrative centre of the borough. Calderdale is served by Calderdale Council, which is headquartered in Halifax, with some functions based in Todmorden. From Wikipedia