Redhill is a town in the borough of Reigate and Banstead in Surrey, England. The town, which adjoins the town of Reigate to the west, is due south of Greater London, and is part of the London commuter belt. The town is also the post town of and an entertainment and commercial area of three adjoining communities: Merstham, Earlswood and Whitebushes, as well as of two small rural villages to the east in the Tandridge District, Bletchingley and Nutfield.
Redhill is sited about 3 miles south of a minor pass at Merstham (elevation of around 120 m (390 ft) compared to a height of around 180 m (590 ft) on either side) in the North Downs, through which passes the London-Brighton road. Beneath this pass, two rival railway companies excavated the Merstham tunnels, which are still used by regular commuter trains and goods transport, with the two railway lines intersecting to the south of Redhill station. A major factor in the development of the town was the coming of the railways. Redhill railway station continues to be an important junction.
A town formed here in part of the rural parishes of Reigate Foreign and Merstham when a turnpike road was built in 1818. The settlement was originally known as "Warwick Town" after Warwick Road, and became known as Redhill when the post office moved from Red Hill Common in the south-west of the town in 1856.
A large, ornate, Victorian psychiatric hospital with well-trimmed grounds, the Royal Earlswood Hospital, initially the Philanthropic Society's farm school for convicts' children, which was first established in 1788 at St. George's Fields, London, relocated to Earlswood in what was the south of Redhill in 1855. Prince Albert laid the first stone in 1853; the hospital was for 40 years home to two of Queen Elizabeth the Queen Mother's cousins Katherine Bowes-Lyon and Nerissa Bowes-Lyon, both of whom had learning difficulties. Another inmate James Henry Pullen (1835–1916) was an autistic savant. He was a brilliant craftsman and artist whose work was accepted by Queen Victoria and Prince Albert. Some of Pullen's ship models, designs and art work used to be on display at the town's Belfry Shopping Centre but have now been moved to the Langdon Down Museum in Teddington. The principal building has been converted to apartments and the renovated grounds provide green open space to balance the large common south-west of Earlswood railway station.
Richard Carrington, an amateur astronomer, moved to Redhill in 1852, and built a house and observatory. Dome Way, where Redhill's only tower block stands, is named after it. The site suited an isolated observatory, being on a spur of high ground surrounded by lower fields and marsh. Here in 1859 he made astronomical observations that first corroborated the existence of solar flares as well as their electrical influence upon the Earth and its aurorae. In 1863 he published records of sunspot observations that first demonstrated differential rotation in the Sun. In 1865 ill health prompted him to sell his house and move to Churt, Surrey.
St John the Evangelist, built in 1843, was the first of Redhill's three Anglican parish churches. The parish originally stretched from Gatton in the north to Sidlow in the south.
The construction, to the east of Redhill, of the M23 motorway between 1972 and 1975 reduced north-south traffic through the town.