Donald James Mackay, 1st Baron Reay, 11th Lord Reay, KT, GCSI, GCIE, PC, FBA, JP, DL (22 December 1839 – 1 August 1921), in the Netherlands known as Donald Jacob, Baron Mackay, Lord of Ophemert and Zennewijnen, was a Dutch-born British administrator and Liberal politician.

[2] After his return to Britain he served as Under-Secretary of State for India between 1894 and 1895 in Lord Rosebery Liberal administration.

Reay strongly opposed this act, and gave the memorable warning: "Oligarchies are seldom destroyed and more frequently commit suicide".

[13] Lord Reay married Fanny Georgiana Jane, daughter of Richard Hasler, of Aldingbourne, Sussex, in 1877.

On his death the barony of 1881 became extinct while he was succeeded in the Scottish title by his cousin Eric baron Mackay (1870–1921) who was succeeded only three months later by his son Sir Aeneas Alexander baron Mackay (1905–1963), 13th Lord Reay, member of the House of Lords (1955–1959).