Derrick Westenra, 5th Baron Rossmore

Derrick Warner William Westenra, 5th Baron Rossmore ( born February 7, 1853 in Dublin, † January 31, 1921, Rossmore Park, County Monaghan ) was a British nobleman and politician.

Derrick Westenra was a son of Henry Westenra, 3rd Baron Rossmore, and his second wife Josephine Julia Helen (nee Lloyd). He had five siblings, three brothers and two sisters. He attended Rugby School and then became an officer.

In 1874 he inherited the title Baron Rossmore of his childless deceased older brother Henry. As such, he was a member of the House of Lords. Furthermore Westenra acted as Justice of the Peace and held the office of Lord Lieutenant of County Monaghan 1887-1921.

In 1882 he married Mittie Naylor. The marriage produced a daughter and two sons were born. His daughter Mary married in 1911 South African businessman Abe Bailey and started later than aviatrix a name.

In 1912 he published his autobiography Things I Can Tell. He died in 1921. Inherited the title of his eldest son William.