List of United Kingdom parliamentary constituencies in Ireland 1801–1885

Under the Acts of Union 1800, with effect from 1 January 1801, there were a 100 MPs representing Ireland in the United Kingdom Parliament. These were divided into 66 constituencies for elections to the United Kingdom Parliament, specified as "two for each County of Ireland, two for the City of Dublin, two for the City of Cork, one for the University of Trinity College, and one for each of the thirty-one most considerable Cities, Towns, and Boroughs":
 * 32 county constituencies, each electing 2 MPs;
 * 33 borough constituencies, each electing 1 MP, except for Cork City and Dublin City, which elected 2 MPs; and
 * 1 university constituency, electing 1 MP.

This distribution remained substantively until 1885, subject to the following alterations:
 * Representation of the People (Ireland) Act 1832: the total number of seats from Ireland increased to 105, with Belfast, Galway Borough, Limerick City, Waterford City and Dublin University gaining a second seat.
 * Parliamentary Boundaries (Ireland) Act 1832: minor boundary changes to the borough constituencies.
 * Representation of the People (Ireland) Act 1868: in the case of boroughs retained under the Municipal Corporations (Ireland) Act 1840, boundaries of parliamentary boroughs extended to include the whole municipal borough.
 * Sligo and Cashel Disfranchisement Act 1870: the boroughs of Cashel and Sligo were disfranchised for corruption, reducing the number of constituencies to 64 and seats to 103.

In the Redistribution of Seats Act 1885, there was a substantial revision of constituencies, taking a greater account of changes to the population. Most borough constituencies were abolished and county constituencies were divided into single-member districts. These new constituencies were first used at the 1885 United Kingdom general election in Ireland.