Greetings Chris:
My personal feeling is that you've missed the prime fall planting window. Moreover, I'm a huge advocate of spring tree planting. Why? Quite simply, I tend to see a lot more “winter kill” (i.e., root/foliar dessication) and frost heaving with fall-planted trees. Some individuals will argue that fall planting is better -- I'll let them argue their point until they’re blue in the face. The simple fact is I’m almost always going to plant my trees during the spring...at least here in Illinois.
Honestly, I'd rather watch my spring-planted tree leaf-out, wither, and die in the scorching heat/drought of summer as compared to unknowingly witnessing my fall-planted tree never having the chance to leaf-out the following spring all while enduring an invisible death at the hands of Illinois’s bone-chilling winter winds/temperatures that can wreak havoc on the delicate roots (and winter foliage of conifiers) of newly transplanted trees.
The obvious caveat here is that if you absolutely need to get the tree(s) in the ground (if you can get the trees in the ground), then by all means go ahead and plant your tree(s). If you're able to hold these trees over using proper storage techniques (or keep the potential transplant in the nursery bed), then I would advise holding off on planting until late winter, early spring.
Oh, you failed to indicate whether you're planting dug transplants, balled and burlapped, or bareroot seedlings!
