Onslow can represent:
- People
- Denzil Onslow (of Pyrford) (died 1721), British politician, Member of Parliament for several constituencies
- Denzil Onslow (British Army officer) (1770–1838), general in the British Army and amateur cricketer
- George Onslow (1784–1853), composer
- Muriel Wheldale Onslow (1880-1932) was a British biochemist
- Earl of Onslow, a British peerage title
- Places
- Onslow, Western Australia
- Onslow, Nova Scotia, Canada and Onslow Speedway
- Onslow Village, an area of Guildford, Surrey, United Kingdom
- Onslow, Iowa, United States
- Onslow County, North Carolina, United States
- Lake Onslow, New Zealand
- Onslow (New Zealand electorate), a New Zealand parliamentary electorate
- Onslow Square, a garden square in South Kensington, London, England
- Other uses
- Onslow College, a secondary school of Wellington, New Zealand
- Onslow AFC, a defunct association football club from Wellington, New Zealand
- HMS Onslow, one of several ships of the Royal Navy
- HMAS Onslow, a submarine of the Royal Australian Navy
- Onslow (Keeping Up Appearances), a character on the British comedy television series Keeping Up Appearances