When we did the Katy last October we started in Clinton, and stayed at the fairgrounds (right behind the community center, right?). We just asked the dudes in the Community Center and they said it was cool if we set up our tent in the fenced in area out back.

Also, I have no connection to this guy, but I would HIGHLY recommend this book... it helped us out a lot on our trip:
http://www.amazon.com/Complete-Katy-...7736052&sr=8-1