Sedgefield District was, from 1974 to 2009, a local government district and, borough in County Durham, in North East England. It had a population of about 87,000. It was named after Sedgefield, but its largest town was Newton Aycliffe. Other places included Shildon, Ferryhill and Spennymoor. The borough was formed, in 1974, under the Local Government Act 1972, by the merger of Sedgefield Rural District, Spennymoor and Shildon urban districts and part of Darlington Rural District.