Leonard Jennett Simpson (July 30, 1882[1] – August 18, 1940)[2] was a physician and political figure in Ontario.

He represented Simcoe Centre in the Legislative Assembly of Ontario from 1929 to 1940 as a Liberal member.

[3] The son of James Simpson and Rachael Jennett, he was born in Thornton, Ontario.

[3] In 1935, he was named honorary president of the Royal Astronomical Society of Canada.

[4] Simpson died in office in Picton, Ontario at the age of 58.