
Irving got it from the MacDonald girl in the late 1820's. Darby really didn't jump on the bandwagon till the late 1830's, but his work was the basis for C.I. Scofield's popularization of dispensationalism in the 1920's. And Scofield was big friends with D.L. Moody of Moody Bible Institute, Chicago. I'm not really sure where Lewis Sperry Chafer, founder of Dallas Theological Seminary, came onboard with Scofield's teaching, but it was pretty early on.
Here's an article that clears up some things. I'm not crazy about Dave MacPherson's attitude, and I think he's also a full preterist, so he has his own errors to deal with. But the information about the origins of dispensationalism/pre-trib rapture looks solid.
