Teesside (/ˈtiːsaɪd/) is a built-up area around the River Tees in the north of England, split between County Durham and North Yorkshire. The name was initially used as a county borough in the North Riding of Yorkshire. Historically a hub for heavy manufacturing, the number of people employed in this type of work declined from the 1960s onwards, with steel-making and chemical manufacturing (particularly through Imperial Chemical Industries) replaced to some extent by new science businesses and service sector roles.