John R. Dethmers (October 15, 1903 – November 1, 1971) was a politician from the U.S. state of Michigan. Dethmers was born in Plessis in O'Brien County, Iowa. He resided in Orange City, Iowa, Holland, Michigan, and East Lansing, Michigan. He enrolled at Hope College in Holland, Michigan, then went on to the University of Michigan Law School and began to practice law in 1927. Dethmers was a member of various judicial associations and was a family man with three children. He was Ottawa County Prosecuting Attorney from 1931 to 1938. He was a member of the Michigan Republican State Central Committee in 1939. Dethmers served as Chairman of the Michigan Republican Party from 1942 to 1945 and was a delegate to the 1944 Republican National Convention. He served as Michigan Attorney General from 19