Southern Ireland (
Irish: Deisceart Éireann) was the larger of the two parts of
Ireland that were created when Ireland was
partitioned under the
Government of Ireland Act 1920. It comprised 26 of the 32
counties of Ireland or about five-sixths of the area of the island, whilst the remaining six counties in the northeast of the island formed
 Southern Ireland included
County Donegal, despite it being the largest county in
Ulster and the most northerly county in all of Ireland.
The Act of 1920, which came into force on 3 May 1921, was intended to create two self-governing territories within Ireland, each with its own parliament and governmental institutions, and both remaining within the
United Kingdom of Great Britain and Ireland. It also contained provisions for co-operation between the two territories and for the eventual reunification of Ireland. However, in the
1921 elections for Southern Ireland's House of Commons,
Sinn Féin candidates were returned unopposed in 124 of the 128 seats, and ignored the parliament, assembling instead as the
 The "
Parliament of Southern Ireland"—consisting of the four
unionist members—met only once.
unrest led to the
Anglo-Irish Treaty and the
Provisional Government which administered Southern Ireland from 16 January 1922 to 5 December 1922: effectively a
transitional administration for the period between the
ratifying of the Anglo-Irish Treaty and the establishment of the Irish Free State. Its legitimacy was disputed by the Anti-Treaty delegates to
Southern Ireland, as a political entity, was superseded by the
Irish Free State (which later became the independent state of
Ireland) on 6 December 1922.