John S. Macdonald

John S. Macdonald may refer to:
 * John Sandfield Macdonald, first Premier of Ontario
 * Harry Macdonough (John Scantlebury Macdonald), Canadian singer and recording executive of the early 20th century
 * John S. MacDonald, Canadian engineer and businessman
 * John Smyth Macdonald (1867–1941), British physiologist