County Antrim is a former county constituency in the House of Commons of the United Kingdom. It was a two-member constituency in Ireland from 1801 to 1885 and in Northern Ireland from 1922 to 1950.

County Antrim had been represented by two seats in the Irish House of Commons. From 1801, under the Acts of Union 1800, it was represented by a county constituency with two MPs in the United Kingdom House of Commons. It consisted of County Antrim, except the parts in the parliamentary borough constituencies of Belfast, Carrickfergus and Lisburn. The boroughs of Antrim and Randalstown were disfranchised in 1801.

In 1885, Carrickfergus and Lisburn were disfranchised and the borders of the parliamentary borough of Belfast were extended. The county was split between the divisions of East Antrim, Mid Antrim, North Antrim and South Antrim.^[1]

In 1922, following the establishment of the Parliament of Northern Ireland, the number of seats in Northern Ireland at Westminster was cut from 30 to 13 under the Government of Ireland Act 1920. The constituency of Antrim was recreated to elect two MPs, consisting of the administrative county of Antrim, that is the whole of County Antrim excluding the part in the city of Belfast.^[2] In 1950, the county was split between the divisions of Antrim North and Antrim South, under the Representation of the People Act 1948, which abolished all multi-member constituencies in the United Kingdom.^[3]

In two-member elections the bloc voting system was used. Voters could cast a vote for one or two candidates, as they chose. The two candidates with the largest number of votes were elected. In by-elections, to fill a single seat, the first past the post system applied.

There was no election in 1801. The representatives of the county in the former Parliament of Ireland became members of the 1st Parliament of the United Kingdom.

After 1832, when registration of voters was introduced, a turnout figure is given for contested elections. In two-member elections, when the exact number of participating voters is unknown, this is calculated by dividing the number of votes by two. To the extent that voters did not use both their votes this will be an underestimate of turnout. If the electorate figure is unknown the last known electorate figure is used to provide an estimate of turnout.

Where a party had more than one candidate in one or both of a pair of successive elections change is calculated for each individual candidate, otherwise change is based on the party vote.