Farnworth is, since 1974, a town and an unparished area within the Metropolitan Borough of Bolton in Greater Manchester, England. It is located 2.3 miles (3.7 km) southeast of Bolton centre, 5 miles (7 km) south-west of Bury, and 9 miles (14.5 km) northwest of Manchester.
Lying within the boundaries of Lancashire since the early 12th century, Farnworth constituted a township and chapelry within the ecclesiastical parish of Deane. In 1837 Farnworth became part of the Bolton Poor Law Union which took responsibility for funding the Poor Law in that area. In 1863, a Local board of health was established for the township, and in 1866, Farnworth also became a separate civil parish. In 1899, under the Local Government Act 1894, Farnworth became an urban district. In 1939, the district was granted by a charter to become the Municipal Borough of Farnworth. In 1974, under the Local Government Act 1972, Farnworth became an unparished area of the Metropolitan Borough of Bolton in Greater Manchester.
Farnworth was originally a hamlet in Barton. In the 13th century it was held by the Lords of Barton and Manchester. By 1320 Adam Lever, Richard Hulton and Richard Redford held the manor as tenants. Later the manor was acquired by the Hultons of Over Hulton. In 1666 there were 91 hearths in Farnworth liable to pay tax. The commons were enclosed in 1798. There was a watermill on the River Croal.
The town expanded rapidly in the 18th and 19th centuries around the coal mining industry. The collieries were part of an extensive mine complex, the Worsley Navigable Levels whose underground canals stretched from the Delph at Worsley and linked the mines to the Bridgewater Canal. Other industry included iron foundries and cotton mills.
The owner of Farnworth Paper mills, T.B. Crompton, patented a continuous-drying process which contributed to the mechanisation of papermaking in 1821.
Farnworth measures about two miles from east to west, and one from north to south with an area of 1,502 acres (608 ha) on land sloping towards the north-east by the River Croal which forms the boundary. Will Hill Brook forms the northern boundary. The underlying rocks are the coal measures of the Manchester Coalfield. Districts in Farnworth include Dixon Green and New Bury. The town has grown along the Manchester to Bolton road, the A666 and the A575 road to Worsley and Eccles.