Stotz, conservation ecologist/ornithologist for the Field Museum, sent Rick this note in response to an inquiry and photo (above) sent:

This is indeed a Sandwich Tern, and is extremely rare in Illinois. There is only one previous record. Laurie Binford found a bird at Waukegan Beach on 26 April 1989. He was the only observer, and unlike you he did not get any photos. His written documentation was excellent and the record was accepted by the records committee. Until your photo, this was the only species accepted on the Illinois srare list without either a specimen or a photo. So this is the second state record and the first with photographic documentation. Great find and great photo.

This morning reports are flying on IBET, the birders network, of a sandwich tern being sighted at Montrose.

I think I am safe in assuming it is the same one.