Hawkeye, yes, raccoons can climb. The one time they got through our pens in Solomon they climbed to the top and found a weak spot in one of the top corners. They are persistent. Also, chicken wire is no match for a raccoon. They will pull and pull and work and work until they get a hole. Welded wire on the outside of the run is a must as far as I'm concerned. Sometimes I will use chicken wire inside my runs to separate pens, but the whole outside has to be welded wire.
Along the outside of the pen, run a foot or so of welded wire around the perimeter. If you pin it down the grass can grow right up through it and you can mow over it. Raccoons and dogs will dig into your pen to get to your birds. They always start right at the edge of the pen, and that is why running the wire down on the ground for about a foot will work.
I generally only have flight netting over the top of my pens, and a raccoon can tear through that... and that is why you need to get out there and trap that raccoon NOW before you get any more poultry. They will tear your chickens apart if they get the chance.