Bacup is a market town and municipal borough in the Rossendale and Darwen parliamentary division of Lancashire, England, on the river Irwell, 203 miles (327 km) north-north-west from London, and 22 miles (35 km) north by east from Manchester. Population (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 1803 by Mr J. H. Maden, M.P., are beautifully laid out. Cotton spinning and power-loom weaving were the chief of numerous manufacturing industries, and there were large collieries in the vicinity.

The borough was incorporated in 1882, and the corporation consists of a mayor, 6 aldermen and 17 councillors. Area, 6120 acres (25 km²), In 1841 the population of the chapelry was only 1526. In the early 1970s the borough of Bacup was merged with nearby towns to form Rossendale Borough.

One of the hills in the vicinity is fortified with a great ancient earthwork and ditch.