Okay, guys, I've checked every single, tiny speck of a town in Colorado and can say, with confidence, that the actual town of South Park doesn't exist. There's not even a South Park County. There is, however, Park County, to the southwest of Denver. Below is a complete list of towns in the southern part of this county:
Hartsel, Balfour, Trump, Guffey, Lake George, Antero Junction, Platte Springs, Tarryall, Garo.
There is also no North Park or Middle Park. My guess is that the guys named South Park for southern Park County, North Park for northern Park County and Middle Park for the area in the middle of Park County, since they both grew up in that county. Just some information I thought I'd pass along, don't kill me for doing the research. :-)