Henry Cairns Westenra, 4th Baron Rossmore (14 November 1851 – 28 March 1874), was an Anglo-Irish soldier and peer who was briefly a member of the House of Lords before his death at the age of 22 in a riding accident.
The son of The 3rd Baron Rossmore (1792–1860) by his second marriage to Josephine Julia Helen Lloyd, the daughter of Henry Lloyd of County Tipperary and of Harriet Amelia Carden, Rossmore was born in 1851.
Lord Rossmore joined the 1st Life Guards, a cavalry regiment of the British Army.
He died in a riding accident on 28 March 1874 and was buried in the family vault at Rossmore Park.
His younger brother Derrick thus succeeded unexpectedly to the titles and estates.