On January 5th 2006 a truck driver and a small time golf park owner witnessed a huge black triangle shaped craft flying low and without any sound. He immediately contacted the local PD and informed them of the sighting. Obviously he was met with the same kinda response that you normally get when you tell someone that you had seen a UFO. Reluctantly they informed the cops on patrol in nearby areas and the cops soon followed up and informed that the craft was indeed there and it was the same as had been described by the first witness. Few patrol cars witnessed the huge craft and recorded their sightings. This was also made available under the FOIA later. This case was also profiled in the Peter Jennings Special two years back.
This case is one of many cases involving strange triangular craft sightings. It has become common belief now amongst the credible UFO research community that these crafts are secret military aircraft and are not out of the ordinary as one might suspect. The now defunct National Institute of Discovery Science (NIDS) investigated the Illinois sightings and indeed concluded that evidence points towards a military aircraft angle.
Anyway this video gives a complete picture of the events that happened on January 5th in Lebanon, Illinois.
I have also linked the original NIDS report rite Here