HORNCastle, a market-town of England, county of Lincoln, on the Bain, a tributary of Witham, and navigable to this point, 18 miles E.S.E. of Lincoln. It was anciently a Roman station, and traces of its old walls still exist. Roman coins and other antiquities have also been discovered in the vicinity. A considerable trade is carried on by means of the river. Horncastle has a grammar school, mechanics' institute, library, literary society, and a savings bank. The market-day is Saturday; and one of the largest horse fairs in the kingdom is held here in August. Pop. (1851) 4921.