I've noticed in the TV series Supernatural there have been quite a few Missouri towns referenced as locations of supernatural events; Carthage, St. Louis, Kansas City, Jefferson City, and even a character named Missouri. As a native Missourian, I find this very interesting and wondered if anyone assoicated with the show has any roots or connections with my home state.
None of the executive producers have anything about Missouri on their Wikipedia pages, and Missouri is right by the center of the continental US (hard to miss in a road trip series like Supernatural), so I'm strongly inclined to say "no".
Besides, you've really only listed 4 out of dozens from just the first 5 seasons.
- There's also 4 places from California: Palo Alto, Jericho, San Francisco, and Los Angeles
- 4 places from Illinois: Chicago (twice), Joliet, Oak Park, and Pontiac (twice)
- 5 named places from Colorado: Lost Creek, Manning, Monument, Rock Ridge, and River Pass. (And one additional one in the list that's just "Colorado")
..And so on. Unless more information pops up, I'm strongly inclined to say that this is just coincidence, where you recognized a place you know - like I recognized Pontiac because I knew someone from there.