William Plender, 1st Baron Plender, GBE, JP, DL (20 August 1861 – 19 January 1946), known as Sir William Plender between 1911 and 1923 and as Sir William Plender, Bt, between 1923 and 1931, was a British chartered accountant and public servant.
Plender was born at Felling, County Durham, the son of William Plender, of The Oaks, Dalston, Northumberland, by Elizabeth Agnes Smallpiece Vardy.
Plender was a partner in Deloitte, Pleander, Griffiths and Company, chartered accountants, and served as President of the Institute of Chartered Accountants between 1910 and 1912. He was knighted in 1911. During the First World War he served as Treasury controller of German, Austrian and Turkish banks confiscated during the conflict from 1914 to 1918 and as financial advisor to the Board of Trade in 1918. He was made a Knight of Grace of the Venerable Order of Saint John (KStJ) and Knight Grand Cross of the Order of the British Empire (GBE) in 1918. He was further honoured in 1923 when he was created a Baronet, of Ovenden in the Parish of Sundridge in the County of Kent, in honour of his "...public services". He was later High Sheriff of the County of London between 1927 and 1928 and High Sheriff of Kent between 1928 and 1929 and was a lieutenant of the City of London. He was once again President of the Institute of Chartered Accountants from 1929 to 1930 and appeared as an expert witness for the defence in the 1931 Royal Mail Case. In January of that year he was raised to the peerage as Baron Plender, of Sundridge in the County of Kent, in recognition of his "...public services". He was also a member of the Committee on National Expenditure headed by Sir George May which published the May Report in July 1931.