There was a boundary change altering this division in 1918, when the new Mid Down constituency was created, and West Down was redefined.
Prior to the 1885 United Kingdom general election and after the dissolution of Parliament in 1922 the area was part of the Down constituency.
Sinn Féin contested the general election of 1918 on the platform that instead of taking up any seats they won in the United Kingdom Parliament, they would establish a revolutionary assembly in Dublin.
In republican theory, every MP elected in Ireland was a potential Deputy to this assembly.
In 1921 Sinn Féin decided to use the UK authorised elections for the Northern Ireland House of Commons and the House of Commons of Southern Ireland as a poll for the Irish Republic's Second Dáil.