Determining exactly which presidents were left handed is a difficult task because during the 18th and 19th century (and even early 20th century), left-handedness was considered a disability. Parents and teachers fought to eradicate any signs of left-handedness in their children and students, and the "condition" rarely lasted beyond childhood.
Therefore, if any presidents were left-handed before the 20th century, we may never know because they may have been forced to give up their natural instincts at a young age.
Examining the presidents that were left-handed reveals interesting connections between being a leftie and becoming president.