We know of at least 13 Presidents of the United States of America have smoked marijuana. That is more than 30% of the men that have been president. Some of them, like Washington are known to have grown the plant at the White House. Unfortunately, for most of our earliest presidents we only know if they smoked based on their journals, so it is very likely that more than 13 have smoked the plant. My favorite part is that Pierce sent a letter to his family saying "the only good thing about the war is the cannabis."
The list includes: Washington, Jefferson, Madison, Monroe, Jackson, Taylor, Pierce, Lincoln, Kennedy, Carter, Bush, Clinton, & Obama