John Edward Cassidy, Sr. (January 31, 1896 – March 25, 1984) was an American lawyer.
Cassidy served in the United States Army in Europe during World War I.
In 1920, Cassidy moved to Peoria, Illinois to head the legal department of Aetna Life Insurance Company.
In 1936, he ran unsuccessfully for the party's nomination for lieutenant governor of Illinois.
In 1947, Illinois Governor Dwight Green appointed Cassidy to be chairman of a citizens committee to investigate the March 25, 1947 mine disaster in Centralia, Illinois.