John Sandfield Macdonald, QC (December 12, 1812 – June 1, 1872) was the joint premier of the Province of Canada from 1862 to 1864. He was also the first premier of Ontario from 1867 to 1871, one of the four founding provinces created at Confederation in 1867. He served as both premier and attorney general of Ontario from July 16, 1867, to December 20, 1871. He was referred to by his middle name, Sandfield, and often signed his correspondence and documents as J. Sandfield Macdonald.