South East Durham was a county constituency represented in the House of Commons of the Parliament of the United Kingdom. It elected one Member of Parliament (MP) by the first past the post system of election between 1885 and 1918.

Barnard Castle was a county constituency centred on the town of Barnard Castle in County Durham, which returned one Member of Parliament (MP) to the House of Commons of the Parliament of the United Kingdom. It was created for the 1885 general election and abolished for the 1950 general election.