Late night brilliant round object following our car for several miles.

This is an absolutely true experience that occurred in 1968, when our son, now 54 and a helicopter flight instructor, were playing in a band with four other junior high school boys.  This more than memorable evening developed after he and the band were finished playing for a birthday party one summer night in Freeport, Illinois, twenty some miles from our homes in Rockford.  Two dad's drove up later that night to pick up the boys and their equipment to bring them back home.  Our son and two other band members were going to ride home in my car.
Incidentally, the other driver headed back home ahead of us as we had several musical instruments, amplifiers and speakers to load into my vehicle.  Shortly after leaving the area, we were back on the main highway, with mostly farmland between Rockford and Freeport.  There was very little traffic at that time and after driving for almost 15-20 minutes, I noticed in the rear view mirror, an extremely bright light coming up behind us on the highway.  I mentioned that to the boys and then stated that it was probably a motorcycle and I wished he would turn off his bright light and flip the dimmer switch. The blinding light continued to remain behind the car for several additional minutes and I couldn't believe the incredible brightness coming from this one single light.  Within a few moments, the light disappeared and I assumed the "rider" had turned off or stopped.
However, in the next couple of minutes, the quietness within the car was broken when one of the boys sitting in the back seat literally shouted "Look outside, next to the road!"  The brilliant round light was now moving parallel to the car, alongside the road on the passenger side, actually following the contour and swales on the ground.  I couldn't judge how close it was to the car, but I imagined about 20-30 yards from the highway.  It was an amazing sight and our "parallel" visitor continued on for at least three or four minutes, staying alongside our car at a speed of about 60 miles per hour.   The next thing to happen was even more unbelievable as the brilliant round object slowly tipped sideways and then accelerated at an incredible speed into the darkness and disappeared.  The boys were really shaken up by this wild incident and I thought I should stop at the Illinois State Police Headquarters a few miles down the road, but they wanted to get straight home.  The UFO story was never reported, but there are four of us "earthlings" that will never forget that summer night and the encounter with a truly unidentified flying object.
I wish a Camcorder was available at that time as it would have been more than newsworthy to quite a few individuals, maiinly the United States Air Force.  (The typical skeptical answer of "It had to be a weather balloon" will definitely not be accepted by this adult and his three witnessess.
((name deleted))
Witness indicates that the date of the incident is approximate.  PD