There is a tiny black-and-orange bird flitting around the birdfeeders in the forest garden. It is mostly dark but with a narrow band of bright orange around its middle and orange edges on the tail. The closest I could find was the black-and-orange flycatcher, but that's in India, which seems ... unlikely. The closest I could find for America was the baltimore oriole, but I have seen those before and it doesn't look much like that. This is smaller and differently patterned. Go figure.
I really hope that some poor flycatcher didn't fall through a wormhole in India and land here. That would not end well.
EDIT 9-7-19: New hypothesis -- American redstart. I have no idea why this did not appear when I searched for black and orange birds in Illinois. Thanks to the folks who suggested this possibility.