This county constituency comprised the central part of County Antrim, specifically the baronies of Glenarm Lower, Toome Lower, part of the barony of Antrim Lower and parts of the parishes of Connor and Ahoghill. It was bounded to the north by Antrim North, to the west by Londonderry South, to the south by Antrim South and Antrim East and to the east by the sea.
The constituency was a predominantly Unionist area. It was also a safe seat for the O'Neill family. All three of the MPs who represented the constituency were related. In 1918 the Unionists defeated Sinn Féin by about 4 to 1.
From 1886 to 1974 the Conservative and Unionist members of the United Kingdom House of Commons formed a single Parliamentary party.
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.