Johnson played the iconic role of Professor Roy Hinkley, whose scientific schemes to get the castaways rescued were always foiled by Gilligan's bumbling.
He died at his home in Washington, where he lived with his wife, Connie. She and their daughter, Kimberly, were at his side, said agent Mike Eisenstadt. Johnson is also survived by a stepson, Court, and a grandson, he said.
Read MoreBefore becoming an actor, Johnson served in the U.S. Army Air Forces during World War II. He was on a B-24 Liberator when it was shot down during a bombing raid over the Philippines in 1945, according to his official biography, and used his G.I. Bill benefits to pay for acting school after the war.