Francis will attend the final two days of the World Meeting of Families on Sept. 26 and 27.
For comparison, the BBC reported the London Olympics required 70,000 volunteers for the two-week Olympiad.
All volunteers must be U.S. citizens and at least 18 years old. Chaput wrote that registration will soon be open on the event’s website.
Organizers are expect up to 2 million people to attend the Pope’s closing mass. That’s 500,000 more than the population of the city.