 Illingworth helped in the business until he was about 20 years old, when he moved to Chicago to study wet plate photography.Shortly after Illingworth's return to St. Paul in 1866, he joined Captain James L. Fisk's fourth expedition to the Montana Territory.Working with photographer, business partner and expedition member George Bill, Illingworth produced 30 stereographs from this expedition that likely became the basis of a gallery and studio that he and Bill opened the following year in St. Paul.