DUBLIN, a county of Ireland, in the province of Leinster, bounded north by Co. Meath, east by the Irish sea, south by Wicklow, and west by Kildare and Meath. The area is 218,873 ac. and the population (1926) 189,248, apart from Dublin city. Of the population over 7o% are Roman Catholics. The county is divided into 10o parishes and its towns include Rathmines, Rathgar, Pembroke, Blackrock. The central and northern por tions of the county are low-lying and composed chiefly of carbon iferous limestone, with some millstone grit to the north and north-west, and some Silurian and Ordovician rocks behind Bal briggan. The peninsula of Howth, connected by a raised beach with the mainland, is formed of old quartzites and shales, crushed and folded, and probably of Cambrian age. The rocks of the county show many signs of ice-action.
The mountains which occupy the southern border of the county are the extremities of the great group belonging to the adjacent Co. Wicklow (q.v.). The principal summits are the group con taining Glendoo (1,919 ft.) and Two Rock (1,699 ft.) within the county, and the border group of Kippure, reaching in that summit a height of 2,473 feet.
The mountains are chiefly covered with heath, except where a subsidence in the ground affords a nucleus for the formation of bog, with which about 2,000 ac. are covered. There are also a few small tracts of bog in the northern part of the county. The mountain district is well adapted for timber. The northern coast of the county from Balbriggan to Howth has generally a sandy shore, and affords only the small harbours of Balbriggan and Skerries. In the promontory of Howth, the coast suddenly as sumes a bolder aspect ; and between the town of Howth and the rocky islet of Ireland's Eye an unsuccessful artificial harbour was constructed. Kingstown harbour on the south side of Dublin bay superseded this, and is by far the best in the county. The chief river is the Liffey, which rises in the Wicklow mountains about 12 M. S.W. of Dublin, and empties itself into Dublin bay. The course of the river is so tortuous that 4o m. may be traversed and only ten gained in direction.
Dublin is among the counties generally considered to have been formed by King John, and comprised the chief portion of country within the English pale. The limits of the county, however, were uncertain, and underwent many changes before they were fixed. As late as the 17th century the mountainous country south of Dublin offered a retreat to the lawless, and it was not until 1606 that the boundaries of the county received definition in this direc tion, along with the formation of county Wicklow. Although so near the seat of government much land was forfeited in the Rebellion of 1641 and in the Revolution of 1688. In 1867 the most formidable of the Fenian risings took place near the village of Tallaght, about 7 m. from the city. Raths or encampments are frequent, and there are also dolmens and round towers.
The extension of Dublin city and its suburbs has no doubt had its influence on the decrease of acreage under both tillage and pasture. Oats and potatoes are the principal crops, but live stock, especially cattle, receives greater attention. A large proportion of holdings are of the smallest, nearly one-half of those beneath 15 ac. being also beneath I acre. The manufactures of the county are mainly confined to the city and suburbs, but there is manufac ture of cotton hosiery at Balbriggan. Fisheries, both deep-sea and coastal, are important, and Kingstown is the headquarters of the fishery district. The salmon fishery district of Dublin also affords considerable employment. The communications of the county are good, several important railways and two canals converging upon the city of Dublin, under the head of which they are considered. Co. Dublin returns eight members to Dail Eireann.