John J. Diehl, Jr. (born August 28, 1965) is an American attorney and a Republican former member of the Missouri House of Representatives.

[3][4] Diehl graduated from De Smet Jesuit High School in Creve Coeur in 1983.

On April 24, 2015, The Kansas City Star contacted Diehl about exchanges of sexually suggestive text messages between himself and a female House intern, who was then a college freshman.

[11] The internship program had been abruptly canceled in April 2015 after Missouri Southern State University discovered an "unspecified incident" with a student, which analysts say was likely Diehl's affair.

[17] In 2023, a Missouri Ethics Commission audit found a bank account Diehl opened in 2015 and held unreported campaign contributions up to $52,000.