Answer:
There is no real town of Bon Temps, LA.
However, you can assume from their descriptions of where the town is, exactly where it would be. Characters from the show often travel to Shreveport and Monroe, and describe Bunkie as being far off to the south. Since Bon Temps is clearly a small rural town, this would most likely put the town somewhere between Winnfield and Jonesboro off of Highway 167 if you are looking at a map.
Of course, don't get your hopes up if you head that way. The town in the show is a sort of mish-mash of every part of Louisiana in both culture and scenery and it's unlikely that you would find this same sort of place (e.g. Cajun accents, Cypress trees with Spanish moss, and voodoo ladies selling exorcisms) in that particular part of the state.
But that's where it would be, if you really want to know. :)
--------other geographic location -----------
Lafayette called and told someone his house was 20 miles away from the emergency room in Monroe. It appears as if Ruston is near, also. When Jason and Crystal tied up the other dude from Hotshot to a tree they call the Sheriff's office and said they were 3 miles from I-20. That puts Bon Temps somewhere between Monroe and Ruston close to I-20. It would probably be between Choudrant and Calhoun, LA. Being close to I-20 would make it a short trip to Ruston, but it would still be about 1 1/2 hour drive to Fangtasia in Shreveport (no problem for Eric, cause the flight time would be quicker!), but that would make more since than putting between Winnfield and Jonesboro or any of the other places it has be speculated at being.