Control channel implies a trunked system. I see only conventional frequencies for St Francis County. The St Francis Co Sheriff has a talkgroup on the AWIN statewide trunked system. What are you unable to receive? Try 159.76.
I would guess they may be utilizing AWIN then. I did a search and am not seeing any licensing for DMR or NXDN for them. Of course, we know that doesn't always mean it isn't being used but it's a good check nonetheless.
I would program up the TGs for St. Francis Co. and see if they are using those or do a wildcard TG search on the closest site and see if there is a new TG that isn't in the db yet.