Donald James Mackay, 11th Lord Reay and 1st Baron Reay (in the Netherlands: Donald Jacob, Baron Mackay, Lord of Ophemert and Zennewijnen) KT, GCSI, GCIE, PC, DL, JP (22 December 1839-1 August 1921) was a Scottish peer and politician. He was born in The Hague in 1839, the son of Aeneas Mackay, 10th Lord Reay (a Dutch government minister) and Maria Catherine Anne Jacoba, daughter of Baron Fagel. He was a British delegate at the Second Peace Conference which led to the signing of the Hague Convention 1907. Other British delegates included Ernest Satow and Eyre Crowe.