I am guessing you are referring to the people that come to watch their last hurrah of rocket launching where they start to head up to Cape Coalwood and the road is lined with cars for over a mile.  It says that as they get closer to the site, they recognized some of the people but not all of them.  Billy remarks that they must be coming from all over the county to watch the launches.

Once they get set up, there is quite a festival there to watch the final launches and probably the best part for Homer is when his father shows up and they allow him to launch the final rocket.