Trivia

MacArthur was the adopted son of actress Helen Hayes and playwright Charles MacArthur. His elder sister, the couple's biological daughter, Mary (for whom he named his own elder daughter), died in 1949 of polio. Hayes established the Mary MacArthur Fund, which helps children with polio along with the March of Dimes. Actress Lillian Gish was his godmother.

Was the final member of the Hawaii Five-O (1968) TV series original cast to pass away.

Stated that one of his favorite Hawaii Five-O (1968) episodes was Retire in Sunny Hawaii... Forever (1975), because he was able to work on screen with his mother, Helen Hayes (who played his Aunt Clara).

MacArthur was in talks to make a cameo appearance on the new Hawaii Five-0 (2010) series, but passed away before the details could be worked out.

MacArthur had four children: Charles Pennock MacArthur, Mary Hayes (MacArthur) McClure, Juliette Nicole (MacArthur) Rappaport, James Duntz MacArthur, and seven grandchildren.

Attended the same high school, Solebury School (New Hope, Pennsylvania) as first wife Joyce Bulifant. They both graduated in the same class (1955).

MacArthur formed a film production company called SouthWind Productions and planned to film his first project called "You Never Gave Me Roses" in the New Orleans area in March 1980. He was to be one of the stars. No evidence the film was ever made.

James was married three times: first wife Joyce Bulifant and second wife Melody Patterson were both actresses, while third wife/widow Helen Beth Durtz was a former LPGA golfer.