John Stephen DeMerit (born January 8, 1936) is an American former professional baseball player from Port Washington, Wisconsin.

Nicknamed "Thumper", DeMerit threw and batted right-handed and was listed as 6 feet 1 inch (1.85 m) tall and 195 pounds (88 kg).

DeMerit appeared in one contest, as a pinch runner for veteran catcher Del Rice in the eighth inning of Game 3.

The Braves left him unprotected in the 1961 National League expansion draft, where he was selected by the Mets with their tenth pick, 20th overall, in the lottery's regular phase.

Following the death of fellow teammate Felix Mantilla, DeMerit is the last surviving member of the 1957 World Champion Milwaukee Braves.