Durham County Council was initially established in 1889 as the upper-tier local authority for the administrative county of Durham. The county council was reconstituted in 1974 as a non-metropolitan county council. Darlington was removed from the area of responsibility in 1997. Durham County Council became a unitary authority on 1 April 2009 when the seven remaining districts of the county (Durham (City), Easington, Sedgefield (Borough), Teesdale, Wear Valley, Derwentside, and Chester-le-Street) were abolished and the county council absorbed their non-metropolitan district functions.
"Durham County Council is the local authority of the non-metropolitan County Durham (i.e. excluding the ceremonial county's boroughs of Darlington, Hartlepool and Stockton-on-Tees, which have their own unitary authority councils) in North East England. Since 2009 it has been a unitary authority, having the powers of a non-metropolitan county and district council combined. From 1889 to 2009 it was a county council in a two-tier arrangement. At the time of the 2011 census it served a population of 513,200, which makes it one of the most-populous local authorities in England. It has its headquarters at County Hall in Durham."