Until 1918 it was bounded to the north-east by South Antrim, to the north-west by East Tyrone, to the west by South Tyrone, to the south by Mid Armagh and to the east by West Down. From 1918 to 1922 the adjoining constituencies were the same, except that North-East Tyrone replaced East Tyrone.
The constituency was a predominantly Conservative then Unionist area. There were few contested elections. In 1918 the Unionists defeated Sinn Féin by about 3 to 1. This was the first contested election for the seat since a 1906 by-election.
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 practice only the Sinn Féin members accepted the offer.
The revolutionary First Dáil assembled on 21 January 1919 and last met on 10 May 1921. The First Dáil, according to a resolution passed on 10 May 1921, was formally dissolved on the assembling of the Second Dáil. This took place on 16 August 1921.