Carysfort was enfranchised by a 1629 charter of 4 Chas I. It was to have a sovereign, 12 burgesses and a free commonalty. At the beginning of the century it belonged to the Allen family. In 1750 Elizabeth Allen, daughter of the 2nd Viscount Allen (0036), married John Proby, 1st Baron Carysfort. This line of the Allen family died out with the 3rd Viscount (0034), and their interest and the major part of their estates (her co-heiress sister, Lady Mayne, died childless) passed through Elizabeth to Proby. In 1757 Lord Carysfort wrote to Lord Lieutenant Bedford that 'The past parliamentary interest of my wife's family is the power of choosing two members for the borough of Carysfort.' In 1783 it had a 'Sovereign, 12 Burgesses, several Freemen without franchise. Patron and Proprietor, Lord Carysfort. Gone entirely to ruin and decay. All electors, of course, non-resident.' In 1790 the borough and its owner were described as follows:
This Borough, of which but one house remains to mark the spot where once a village stood, is the property of the Earl of Carysfort, who appointing the twelve Burgesses, the only electors remaining to it, through the medium of them, constantly nominates its representatives, Though almost invariably an absentee, for many years past he has not sold it, but returned two of his connections for it. The noble Earl having found by experience that he can traffic with the minister more advantageously by wholesale, than by retail. An elevation of title and a considerable sinecure employment, both recently acquired, evince his skill in political calculation.453
John Joshua, the son and heir of the 1st Lord Carysfort and Elizabeth, Lady Carysfort née Allen, was created Earl of Carysfort in 1789.
Carysfort was disfranchised by the Act of Union; the £15,000 compensation was duly paid to the Earl of Carysfort.