a county of Ireland, in the province of Connaught, bounded on the west by the river Suck, on the east by the Shannon, on the north by the Curlew mountains, on the south and south-east by the King's-county and part of Galloway. Its length is 35 miles, its breadth 28. The air of the county, both on the plains and mountains, is healthy; the soil yields plenty of grass with some corn, and feeds numerous herds of cattle. The Curlew mountains on the north are very high and steep; and, till a road with great labour and difficulty was cut thro' them, was impassable.

Roscommon, which gives the title of earl to the family of Dillon, and name to the county, tho' not large, is both a parliamentary borough and the county town.

(Wentworth Dillon, earl of), a celebrated poet of the 17th century, was the son of James Dillon, earl of Roscommon; and was born in Ireland, under the administration of the first earl of Strafford, from whom he received the name of Wentworth at his baptism. He passed his infancy in Ireland; after which the earl of Strafford sent him into England, and placed him at his own seat in Yorkshire, under the tuition of Dr Hall, afterwards bishop of Norwich, who instructed him in Latin, without teaching him the common rules of grammar, which he could never retain in his memory, and yet he learnt to write in that language with classical elegance and propriety. On the earl of Strafford's being impeached, he went to complete his education at Caen, in Normandy; and after some years travelled to Rome, where he became acquainted with the most valuable remains of antiquity, and in particular was well skilled in medals, and learned to speak Italian with such grace and fluency, that he was frequently mistaken for a native. He returned to England soon after the restoration, and was made captain of the band of pensioners; but a dispute with the lord privy-seal, about a part of his estate, obliged him to resign his post and revisit his native country, where the duke of Ormond appointed him captain of the guards. He was unhappily very fond of gaming; and as he was returning to his lodgings from a gaming-table in Dublin, was attacked in the dark by three ruffians, who were employed to assassinate him. The earl defended himself with such resolution, that he had dispatched one of the aggressors, when a gentleman passing that way took his part, and disarmed another, on which the third sought his safety in flight. This generous affianced was a disbanded officer of good family and fair reputation, but reduced to poverty; and his lordship rewarded his bravery by resigning to him his post of captain of the guards. He at length returned to London; when he was made master of the horse to the duchess of York, and married the lady Frances, eldest daughter of Richard earl of Burlington, who had been the wife of colonel Courtney. He distinguished himself by his writings; and in imitation of those learned and polite assemblies with which he had been acquainted abroad, began to form a society for refining and fixing the standard of the English language, in which his great friend Mr Dryden was a principal assistant. This scheme was entirely defeated by the religious commotions which ensued on king James's accession to the throne. In 1683 he was seized with the gout; and being too impatient of pain, he permitted a bold French pretender to physic to apply a repelling medicine, in order to give him present relief; which drove the distemper into his bowels, and in a short time put an end to his life in 1684. He was a man of an amiable disposition, as well as a good poet: his poems, which are not numerous, are printed in the first volume of the works of the minor poets.