John Johnston Lefferty (ca 1777 – October 26, 1842) was a doctor and political figure in Upper Canada.
He was born in New Jersey around 1777 and settled in the Niagara region of Upper Canada in 1797.
He served as a surgeon for the militia during the War of 1812; his home was burned by American troops.
In 1830, he introduced a bill that would allow magistrates to enforce observation of Sunday as a religious day.
In 1834, he was initially declared reelected in 3rd Lincoln, but was unseated when his opponent, David Thorburn, successfully appealed to the Legislative Assembly.