It was in the northern area of County Dublin (later Fingal), and included the towns of Balbriggan and Malahide, Lusk, Rush, Donabate and Skerries.

Balbriggan Rural, Balbriggan Urban, Ballyboghill, Balscadden, Blanchardstown (except the part thereof which is comprised in the constituency of Dublin West), Clonmethan, Donabate, Finglas (except the parts thereof which are comprised in the constituencies of Dublin North-West and Dublin West), Garristown, Hollywood, Holmpatrick, Kilsallaghan, Kinsaley, Lusk, Malahide, Rush, Skerries, Swords East and Swords West; and the townlands of: Ballymacartle, Bohammer, Burgage, Clonshagh, Maynetown, Saintdoolaghs, Snugborough, in the district electoral division of Coolock; Coultry, Ballymun, Huntstown, Silloge, in the district electoral division of Drumcondra Rural Number One; and part of Blanchardstown from Dublin County West Balbriggan Rural, Balbriggan Urban, Balgriffin, Ballyboghil, Balscadden, Clonmethan, Donabate, Garristown, Hollywood, Holmpatrick, Kilsallaghan, Kinsaley, Lusk, Malahide East, Malahide West, Portmarnock North, Portmarnock South, Rush, Skerries, Swords-Forrest, Swords-Glasmore, Swords-Lissenhall, Swords-Seatown, Swords Village; and those parts of the electoral divisions of Airport, Dubber, Priorswood A, Priorswood B, Priorswood C, The Ward and Turnapin situated north of a line drawn as follows: Balbriggan Rural, Balbriggan Urban, Balgriffin, Ballyboghil, Balscadden, Clonmethan, Donabate, Garristown, Hollywood, Holmpatrick, Kinsaley, Lusk, Malahide East, Malahide West, Portmarnock North, Portmarnock South, Rush, Skerries, Swords-Forrest, Swords-Glasmore, Swords-Lissenhall, Swords-Seatown, Swords Village; Note: The columns in this table are used only for presentational purposes, and no significance should be attached to the order of columns.

Following the election of Independent TD Alfie Byrne to Seanad Éireann, a by-election was held on 14 March 1929.

Following the disqualification of Irish Worker League TD James Larkin due to bankruptcy, a by-election was held on 3 April 1928.

Following the resignations of Cumann na nGaedheal TDs Francis Cahill and Seán McGarry, a by-election for both seats was held on 11 March 1925.