Douglas Harper's Etymology Dictionary
post-millennial
also postmillennial, 1831, from post- "after" + millennial; chiefly in reference to the Protestant doctrine that the second coming of Christ will occur after, not at, the Christian millennium.
Usage examples of "post-millennial".
The underlying theology seemed to be Celtic, but it was mixed in with a bit of New Age, a bit of post-millennial anxiety, a lot of sci-fi stuff about UFOs.