Borough of Darlington: History
The town of Darlington was made a municipal borough in 1867. In 1915 it was elevated to become a county borough, taking over county-level functions from Durham County Council.
The borough was reformed and enlarged on 1 April 1974 under the Local Government Act 1972. It absorbed nearly all of the surrounding Darlington Rural District, with the exception of the parish of Great Aycliffe (which covers the town of Newton Aycliffe) which went to Sedgefield district. The enlarged borough was also reconstituted as a non-metropolitan district as part of the 1974 reforms, with Durham County Council once more providing county-level services to the town.
The council was made a unitary authority on 1 April 1997, regaining its independence from the county council. The way this change was implemented was to create a new non-metropolitan county of Darlington covering the same area as the existing borough, but with no separate county council; instead the existing borough council took on county functions, making it a unitary authority. The borough remains part of County Durham for ceremonial purposes, with whom it continues to share certain local services, such as the County Durham and Darlington Fire and Rescue Service and Durham Constabulary.
Since 2016 the council has been a member of the Tees Valley Combined Authority along with Hartlepool, Middlesbrough, Redcar and Cleveland and Stockton-on-Tees. Unlike Darlington, the other four districts in the combined authority had all been part of the county of Cleveland between 1974 and 1996.