Complex sentence: Frantz was established in Sterling, Illinois once known as the "The Hardware Capital of the World" and is cited by the Sterling-Rock Falls Historical Society as one of four major manufacturing facilities that showed strong growth in the mid to late 20th Century.
Split into simpler sentences: Frantz was established in Sterling, Illinois which was once known as the "The Hardware Capital of the World". It is cited by the Sterling-Rock Falls Historical Society as one of four major manufacturing facilities that showed strong growth in the mid to late 20th Century.