Apparently, Ken Brock has found an adult-plumaged Arctic Tern at the Lake Street Beach in Gary, Indiana, not too far from Chicago.
This reminds me of the Arctic Tern that was at Great Lakes in Illinois a few years back. I tried several times and never saw it, just bad luck on my part, I guess; one time I was there for a few hours and a number of birders came by and ticked a tern as an Arctic Tern that was clearly nothing more than your average Common Tern. Sometimes people see what they want to see.
UPDATE: The Arctic Tern was apparently still present at 2:30. A Little Gull was also seen at Miller Beach today.
UPDATE: Today (Saturday) the Arctic Tern and a Little Gull have both been relocated.