Since the ban has been lifted (9/08), these are some states where they are not permitted: OH, WI, CA, CO, MA, PA, GA, MS, OR, and more.
Every year laws change. Due to my work, I help a portion of my clients throughout the country that either want them as captive pets or are looking toward relocation to determine the current legality of prairie dogs as pets.
Some states simply aren't aware that ban restrictions were lifted September, 2008.
I'm happy to help anyone with this process because it is not as cut and dry and sometimes, if you don't know how to approach it, they will simply tell you no as a means of disallowing a species they may not prefer people to keep instead of actual laws or regs that prohibit them as pets.