The Municipal Borough of Farnworth was a local government district centred on the town of Farnworth in the administrative county of Lancashire, England. A local board of health had been established for Farnworth in 1863, which was reconstituted as an urban district in 1899, before being granted a charter of incorporation to become a municipal borough in 1939. Following abolition of the local authority in 1974, Farnworth became an unparished area of the Metropolitan Borough of Bolton in Greater Manchester.