Earl of Onslow, of Onslow in the County of Shropshire and of Clandon Park in the County of Surrey is a title in the Peerage of the United Kingdom. It was created in 1801 for George Onslow, 4th Baron Onslow.

The Onslow family descends from Arthur Onslow, who represented Bramber, Sussex and Guildford in the House of Commons. He was the husband of Mary, daughter of Thomas Foote, Lord Mayor of London in 1649, who had been created a Baronet in 1660 (a title which became extinct on his death in 1687). In 1674, Onslow was himself created a Baronet in the Baronetage of England, with the precedence of 1660.

Onslow was succeeded by his son, the second Baronet. He was a prominent politician and served as Speaker of the House of Commons from 1708 to 1710 and as Chancellor of the Exchequer from 1713 to 1714. In 1716 he was raised to the Peerage of Great Britain as Baron Onslow, of Onslow in the County of Shropshire and of Clandon Park in the County of Surrey,^[1] with remainder, failing male issue of his own, to his uncle Denzil Onslow, and afterwards, to the male heirs of his father. Lord Onslow was succeeded by his son, the second Baron. He sat as Member of Parliament for Gatton, Chichester, Bletchingley and Surrey and served as Lord Lieutenant of Surrey. His son, the third Baron, represented Guildford in Parliament and served as Lord Lieutenant of Surrey. He was heirless on his death in 1776.

Lord Onslow was succeeded according to the special remainder by his second cousin and heir male of his great-grandfather, who became the fourth Baron. He was the son of Arthur Onslow, Speaker of the House of Commons, elder son of Foot Onslow. He was Member of Parliament for Rye and Surrey and notably served as Treasurer of the Household and as Lord Lieutenant of Surrey. In May 1776, five months before succeeding in the barony of Onslow, he was raised to the Peerage of Great Britain in his own right as Baron Cranley, of Imber Court in the County of Surrey.^[2] In 1801 he was further honoured when he was made Viscount Cranley, of Cranley in the County of Surrey, and Earl of Onslow, of Onslow in the County of Shropshire.^[3] The latter titles were in the Peerage of the United Kingdom. A grandson, André George Louis Onslow (1784–1853), was a noted composer, and author of thirty string quartets and other works.

His son, the second Earl, represented Rye and Guildford in the House of Commons. He was succeeded by his eldest son, the third Earl. He died without surviving male issue and was succeeded by his great-nephew, the fourth Earl. He was the son of George Augustus Cranley Onslow, son of Thomas Cranley Onslow, second son of the second Earl. Lord Onslow was a prominent Conservative politician and served as Under-Secretary of State for the Colonies, as Under-Secretary of State for India and as President of the Board of Agriculture and was also Governor of New Zealand. His eldest son, the fifth Earl, was also a Conservative politician. He notably held office as Under-Secretary of State for War and as Paymaster General during the 1920s.

He was succeeded by his son, the sixth Earl. He served in the Conservative administrations of Winston Churchill, Anthony Eden and Harold Macmillan as Captain of the Yeomen of the Guard (Deputy Chief Whip in the House of Lords) for nine years. From 1971 to 2011, the titles were held by his son, the seventh Earl, who succeeded in 1971. The seventh Earl was one of the ninety elected hereditary peers who remained in the House of Lords after the passing of the House of Lords Act 1999, and sat like his ancestors on the Conservative benches. He is the only hereditary peer to have appeared as a panellist on Have I Got News For You. Upon his death on 14 May 2011,^[4] he was succeeded by his son, now the eighth Earl, who inherited Clandon Park, the 1000-acre agricultural Parkland Estate in Surrey in January 2017.

Another member of the Onslow family was the Conservative politician Cranley Onslow. He was a descendant of George Onslow, eldest son of Lieutenant-General Richard Onslow, nephew of the first Baron and uncle of the first Earl. Also, Admiral Sir Richard Onslow, 1st Baronet, was the second son of Lieutenant-General Richard Onslow. See Onslow baronets of Althain for more information on this branch of the family.

The family seat of the Earls of Onslow is Clandon Park in Surrey. Although Clandon House and gardens were gifted and endowed by the Onslow family to the National Trust in 1955, the surrounding agricultural estate called Clandon Park, covering over 1,000 acres and including areas of Grade II-listed parkland, remains in the ownership of The Earl and Countess of Onslow.

The eighth Earl married Leigh Jones-Fenleigh, at Oakham on 10 September 1999 and they have one daughter.

The family's coat of arms is: Argent a fess gules between six Cornish choughs proper. The supporters are two falcons, proper, belled or. The crest is made up of an eagle sable preying on a partridge or. The motto is "FESTINA LENTE" (Latin: Make haste slowly), although "SEMPER FIDELIS" (Always faithful) is also used.^[5] The coat of arms is the basis of the badge of Onslow St Audreys School in Hatfield, Hertfordshire.^[6]

• Sir Arthur Onslow, 1st Baronet (1622–1688)
• Sir Richard Onslow, 2nd Baronet (1654–1717) (created Baron Onslow in 1716)