LLANGEFNI, a parliamentary borough and market-town of Wales, county of Anglesea, is situated in a fertile vale on the River Cefni, about 15 miles E.S.E. from Holyhead. At its annual fairs great numbers of cattle are sold for the English market. In the vicinity there are vestiges of a paved road supposed to be Roman. The borough is contributory to Beaumaris. Pop. (1851) 1362.