Johannes "Jan'" de Klerk, DMS (22 July 1903 – 24 January 1979) was a South African politician. He was the father of Frederik Willem de Klerk, the last State President of South Africa.
As a member of the National Party, de Klerk served as interim State President for nine days following the retirement of Jacobus Johannes Fouché in 1975. Prior to this, he served as a Senator (1955–1975), Minister of Work and Public Works (1954–1958), Work and Mines (1958–1961), Home Affairs, Work and Immigration (1961), Home Affairs, Education and Arts and Sciences (1961–1966), Education, Arts and Sciences and Information (1966–1967) and National Education (1968–1969), and President of the Senate from 1969 to 1976.
Son of Reverend Willem de Klerk and his wife Aletta Johannes van Rooy, Jan de Klerk was born 22 July 1903 in Burgersdorp. He spent his childhood in Potchefstroom, in South-West Transvaal. Graduating from Potchefstroom University (1926) where he was the President of the Student Union, he married Hendrina Cornelia Coutzer on 27 April 1927, and had two sons, Willem Johannes and Frederik Willem.
