Farnworth is a town, 2.3 miles (3.7 km) southeast of Bolton, 4.3 miles south-west of Bury (7 km), and 7.5 miles (12.1 km) northwest of Manchester.

Historically in Lancashire, Farnworth lies on the River Irwell and River Croal. At the 2011 Census, it had a population of 30,271.

Farnworth derives from the Old English fearn, fern and worth an enclosure. Farnworth was recorded as Farneworth and Farnewrth in 1278 and 1279 and Ffornword in a land survey of 1282.

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.

The adjoining open land of Halshaw Moor became an area for recreation for the town, hosting the annual Halshaw Moor Wakes that were described as

a saturnalia which was first celebrated in September, 1827, when bull-baiting, badger-baiting, dog fighting, cock fighting, foot racing in almost a state of nudity, grinning through a horse collar, eating a dishful of scalding hot porridge without milk and feeding themselves with their bare hands, and even the more disgusting exhibition of eating a pound of tallow candles, and stripping the wicks through their teeth for wagers, were amongst the orgies on these occasions.