Yeah, unfortunately you're mostly out of luck for monitoring Colleton County public safety. Sheriff's office, Fire and EMS are almost entirely encrypted. I haven't monitored extensively there, only when passing through on I95. I believe that Walterboro PD is in the clear, oddly enough. Perhaps Walterboro FD is also, if they're an entity separate from the County fire department.
FYI the Edisto Island site appears to be part of the Charleston County "section" of the system. This means that you won't hear the common state and surrounding agencies. If you're in range to receive that site, likely you'll hear some Charleston County talkgroups (where law enforcement is also encrypted) along with Edisto Island agenciees. I believe Edisto is in the clear.
If you're closer to the Canadys site, you'll likely hear a good bit of Dorchester County radio traffic, if that's of interest at all.
You might get a better response by requesting to move this thread to the South Carolina forum.