Blessington was incorporated by a 1670 charter, 21 Chas II. The corporation comprised a sovereign, two bailiffs and 12 burgesses and as many freemen as they thought fit. In 1783 the borough was described as follows: '12 Burgesses, choose a Portrieve, 2 Bailiffs and Registrar out of themselves. There are 5 Freemen who vote at elections. Election, by Charter, in the Hall of Blessington House. Patron and proprietor, Lord Hillsborough. 240 inhabitants. Power to make Freemen which is not exercised. All electors are non-resident, except for the sovereign and bailiffs. A corrupt, venal and rotten Borough at the absolute command of the Patron.' In 1790 Blessington was a 'neat little town, built and ornamented by Primate (1679-1702) Boyle, was long possessed by his descendants in the female line, who derived the title of Earls from it but is now, by various devolutions, the property of the Marquess of Downshire (1016). As the electors here consist only of the twelve Burgesses, who are uniformly chosen agreeably to his Lordship's pleasure, it is evident that the Marquess is the appointer of its nominal representatives.' Primate Boyle was succeeded by his son Murrough, created Viscount Blessington, and from him it descended through his daughter to Charles Dunbar (0666) who, dying childless in 1778, bequeathed his estates to the descendants of Primate Boyle, one of whose great-great-grandsons was Lord Hillsborough. Other beneficiaries were Lords Longford and De Vesci, but the Blessington estate came to Lord Hillsborough, later 1st Marquess of Downshire. Blessington was disfranchised by the Act of Union and the £15,000 was paid to the estate of Arthur, 2nd Marquess of Downshire.