The New York Post's Pop Wrap blog reports that the trio will workshop the musical, which is titled Mormon Musical.
Cheyenne Jackson, who has been cast in the workshop, told the Post, "It's hilarious - very acerbic and biting. It offends everybody but does what 'South Park' does best, which is by the end it comes around and has something great to say."
No official information has been announced about the Mormon Musical.
Cheyenne Jackson, who was seen in the film "United 93," has appeared on Broadway in Xanadu, All Shook Up, Aida and Thoroughly Modern Millie. He starred in the premiere cast of Altar Boyz, and his regional credits include West Side Story, The Most Happy Fella, Children of Eden, Hair, Carousel, Damn Yankees and Kismet. Jackson is a member of the Broadway Inspirational Voices and was seen Off-Broadway in The Agony and the Agony and at City Center in Damn Yankees.