Derrick Westenra, 5th Baron Rossmore

Derrick Warner William Westenra, 5th Baron Rossmore (7 February 1853, Dublin, County Dublin, Ireland – 31 January 1921, Rossmore Park, County Monaghan, Ireland), was an Anglo-Irish noble, soldier and author.

Biography
The son of The 3rd Baron Rossmore and Josephine Julia Helen (née Lloyd), he was educated at Rugby. He gained the rank of Sub-Lieutenant in 1872 in the service of the 9th Lancers. He gained the rank of Sub-Lieutenant in 1874 in the service of the 1st Life Guards.

He succeeded to the title of 5th Baron Rossmore, of Monaghan in the County of Monaghan, on 28 March 1874. He retired from the military in 1876. He held the rank of Honorary Colonel in the service of the Monaghan Militia. Lord Rossmore held the office of Lord-Lieutenant of County Monaghan between 1887 and 1921. He wrote the book Things I Can Tell, published 1912.

He was one of the first polo players in England, where he played in Richmond Park in London.

Family
He married Mittie Naylor on 14 June 1882 at All Saints' Church, Ennismore Gardens, London, England.

Children:
 * The Hon. Dame Mary Bailey (born 1 December 1890 – died 29 July 1960)
 * William Westenra, 6th Baron Rossmore (born 12 July 1892 – died 17 October 1958)
 * The Hon. Richard Westenra (born 15 October 1893 – died 26 July 1944)