John R. Dethmers (October 15, 1903 – November 1, 1971) was a politician from the U.S. state of Michigan.

[1] Dethmers was born in Plessis in O'Brien County, Iowa.

Dethmers was a member of various judicial associations and was a family man with three children.

He was a member of the Michigan Republican State Central Committee in 1939.

Governor Harry Kelly appointed Dethmers Justice of the Michigan Supreme Court, serving from 1946 to 1970 and serving as Chief Justice of the Michigan State Supreme Court in 1953, 1956–1962, and 1967–1969.