The last post is close, but Cat no longer owns the plant either. The factory in Dekalb, IL is owned by AGCO, and the employees are paid by AGCO. Cat still makes several of the components that go into the tractors like the tracks, engines, transmissions, cabs, electronics, etc. Those all come from separate facilities owned by Cat. Cat has like a 5 year contract with AGCO to supply these components, after that AGCO is free to do what they will with the tractors.
The Challenger AG equipment is almost identical to AGCO equipment, with different paint, decals, and engines. I would like to see Cat start to sell more engines and components to AGCO for all of their equipment, and I think Cat hopes to too. At this point Cat doesn't have much to do with the Challenger brand, its up to the individual Cat dealers to sign up with AGCO to carry the line, not Caterpillar. Its similar to a Ford dealer signing up with Chrysler to carry the Jeep brand for example. Some dealers are choosing to do that, some are not, its their option.