Sorry for the belated report everyone.
On Monday ( 3 Oct) I quickly stopped in Primm to check out the Forest Preserve before an obligation in Vegas.
There I observed a Tropical/Couch's type Kingbird in the lawn patch. The Kingbird had a large bill, a notched tail without any white on the edge of the outer rects, a very yellow underside extending high up into it's breast which contrasted with it's white throat, and a darkish mask extending behind the eye. Knowing that the two aforementioned species are most reliably distinguished by call/song, I used playback of both Tropical, Couch's, and Western. Alas, the bird did not respond to that or when I was stalking it around as it sallied for insects. Unfortunately, a late night arrival on Sunday from the Bay made me not restock my car with my camera (which makes complete sense why I saw this bird *sigh*), and all photos are from my phone. They can be seen here:
I will upload a few more once they are cropped for eBird purposes.
A group of skilled birders returned yesterday morning to refind the bird but with no luck. A.Harper did see a "yellow-bellied" kingbird in the gated off apartment complex, but access was prohibited. I also returned for another 2 hours later in the afternoon, also with no love.
A good chance this bird could be hanging around the area and I just wanted to get the word out there.