LLANFYLLIN, a small market-town and parliamentary borough of Wales, in Montgomeryshire, on the River Cain, an affluent of the Vyrnwy, 17 miles N.N.W. from Montgomery. The two chief edifices, both built of brick, are the town-hall and the church, the latter erected in the Venetian style, and possessing a fine peal of bells. The town is celebrated for its ale. Some Roman coins have been found here. The market-day is Thursday. There are six annual fairs, at which the celebrated "merlins," or Welsh ponies, are sold in great numbers. The borough is contributory to Montgomery. Pop. (1851) 1116.