Sir William Frederick Coates, 1st Baronet (1866 – 19 January 1932) was an Irish and politician in Belfast.
Coates was born in Belfast and studied at the Royal Belfast Academical Institution. He initially entered the linen trade, but became a stockbroker in 1887, building up an extensive business. In 1902 he was elected to Belfast Corporation. He was chairman of the finance committee from 1917 and was elected Lord Mayor of Belfast in 1920 and then re-elected twice, serving until 1923.
He hosted the King and Queen when they visited Belfast to open the Parliament of Northern Ireland (of which he was also a Senator, both ex officio as Lord Mayor and as an elected member 1924-1929) in July 1921. For hosting the monarchs, and guiding Belfast past the sectarian conflict that marked the creation of Northern Ireland in the early 1920s, Coates was created a Baronet. He served as Lord Mayor again from 1929 to 1931.
He served as High Sheriff of Belfast (1906–1907) and as High Sheriff of Antrim (1931–1932).