Bacup, a market town and municipal borough in the Rossendale parliamentary division of Lancashire, England, on the river Irwell, 203 m. N.N.W. from London, and 22 N. by E. from Manchester, on the Lancashire & Yorkshire railway. Pop. (1901) 22,505. It is finely situated in a narrow valley, surrounded by wild, high-lying moorland. It is wholly of modern growth, and contains several handsome churches and other buildings, while among institutions the chief is the mechanics' institute and library. The recreation grounds presented in 1893 by Mr. J. H. Maden, M.P., are beautifully laid out. Cotton spinning and power-loom weaving are the chief of numerous manufacturing industries, and there are large collieries in the vicinity. The principle of co-operation is strongly developed, and a large and handsome store contains among other departments a free library for members. The borough was incorporated in 1882, and the corporation consists of a mayor, 6 aldermen and 17 councillors. Area, 6120 acres. In 1841 the population of the chapelry was only 1526. One of the hills in the vicinity is fortified with a great ancient earthwork and ditch.