There was a Crested Caracara sighted in Kankakee this morning, a county just south of Chicago.
There will be a lot of discussion about the origin of this bird.
However, I think it would be a mistake to automatically assume the bird is an escapee. The link provided by Tom Kelly on the Illinois birding list (from Don Roberson's web site) is quite informative, and refers to at least a couple of vagrant Caracara records that appear to be legitimate. The one problem with a theory of natural vagrancy for this bird is that the time period is not really right, the other vagrant records were summer birds.
This species is undergoing a range expansion, and it would be important for other observers to try to relocate this bird and take photos that would show any indication of captivity or falconry.
As far as zoo escapes are concerned, it is pretty easy to use ISIS to determine that there are only three known Caracaras currently being held in the Midwest (two in Grand Rapids and one in St. Louis) and it would only take a couple of calls to confirm that those birds have not flown the coop, so to speak. And while a Caracara could certainly be kept by a falconer, that would seem fairly unlikely, since Caracaras are partially carrion eaters. So hopefully someone will relocate this bird.