Haydock is a village within the Metropolitan Borough of St Helens, in Merseyside, England. At the 2011 Census, it had a population of 11,416 Haydock's historic area covers the Haydock electoral ward and a section of the Blackbrook ward.

Haydock is located within the boundaries of the historic county of Lancashire. The village is located to the north-east of the adjacent St Helens, with most of its residential estates and commercial property built either side of the A599. Historically a township and large pastoral area, Haydock was found to be rich with coal and the area grew in significance during the Industrial Revolution particularly with the coming of the canals and railways. In the 1930s, the north side of Haydock was bisected by the A580 East Lancashire Road; this dual carriageway connected the cities of Liverpool and Manchester, with several junctions serving St Helens and Haydock. The area to the south of the East Lancs road saw large post-war residential development, while the area to the north, that was initially open pits, saw large scale industrialisation. More recently, the area north of the road has seen the development of distribution centres encouraged by the proximity of junction 23 of the M6 motorway and Haydock's convenient transport links to Liverpool and Manchester.

Haydock is the home of the Haydock Park Racecourse, while the old mining tip and spoil areas south of the village have been developed into the Lyme & Wood Pits Country Park.

The placename means "barley, wheat" with the suffix -aco meaning "place". An undated source refers to the name as Heidiog. The village is often referred to by the colloquial name of 'Yick', and its inhabitants may be referred to as 'Yickers' .

Haydock was one of the United Kingdom's richest areas in coal and coal mining, Haydock Collieries had up to 13 collieries working at one time. The last colliery in Haydock – Wood Pit – closed in 1971, bringing to an end coal mining in the area. This site had been the scene of the Wood Pit disaster on 7 June 1878 which a subsequent report of the Inspector of Mines concluded claimed the lives of 189 men and boys. Among them were forty-five-year-old Nathan Boon and his five sons. According to GenUKI, 15 victims were not included in the Inspector's report but their names "appeared in the Coroner's Inquest and in some cases in the burial registers". If included, the final death toll would have been 204.

The Old Boston Trading Estate was built atop the colliery of the same name in the north of Haydock. After the colliery was closed, due to an underground fire, the site was used for many years as a training centre for National Coal Board employees.

Surrounded by agricultural farmland, much of the village's expansion was due to mining and canal transport. In the early 1900s, Haydock had no fewer than three railway stations–Haydock, Ashton-in-Makerfield, and Haydock Park–along the line which passed through from St. Helens to Lowton.

Haydock was a township in the parish of Winwick before being made a civil parish in 1866. The village was in the poor law union of Warrington in the 19th century before being created an urban district in 1894.