It looks like a common garter snake to me. There are several varieties. I hope you didn't kill it as they good snakes. Here is a link to enature.com. They have field guides where you can look up almost enything. I have linked to garter snakes. You may find yours there. Sorry it is long, but I narrowed it down to southest, then common garter snake. there are serveral pictures and one of them looks like yours http://enature.com/fieldguides/detail.asp?source=&parkid=&searchText=garter+snake&allSpecies=y&shapeID=0amp;lshapeID=0amp;curAbbr=&lastView=default&lastGroup=7&lastRegion=&lastFilter=4&lastShapeName=&trackType=&curRegionID=2209&size=&habitat=&fruit=&color=&sortBy=family&curFamilyID=®ionSelect=Southeast®ionZIP=&curGroupID=7&lgfromWhere=&curPageNum=1

Every since I learned that if you see rat snakes you have unseen rats and mice; and if you kill rat snakes venenmous snakes will move in to take their place, I have been content to leave the rat snakes alone. We all have a reflex action, a natural inborn protective mechanism, to jump back when we see a snake, but then reason takes over with the realization that some snakes are doing a good job for us. Interestingly it's against the law in India to kill cobras, one of the most venomous of all snakes, because they control rats. There are several other small and medium size harmless snakes we might see in the garden. Familiarize yourself with snakes and remove the fear. The first thing I do when I see a snake is look for the very wide jaws of copperheads, rattle snakes and water moccasins, the three venonmous snakes. If it has the more narrow head it's okay. My friend Barbara had a phobia, an unreasonable fear, of spiders. Her doctor suggested she wear some beautiful jewelry in the form of a spider. Barbara loves jewelry and began to collect spider pins and rings. That did it. She overcame her panicky fear of spiders. So perhaps if one has an unreasonable fear of snakes a jeweled snake pin would be a nice gift to yourself. Do you suppose that is the secret reason that some men wear snake skin belts and scorpion belt buckles??? Happy gardening! :-)

Jonesella - NO! Not poisonous. They will bite if you pick them up wrong, and it hurts, but they have no venom. Racers eat rodents and insects and small birds. Good things to have around your landscape. Not so good around a chicken coop if you have tiny chicks, but you can use screens and keep them out until the chicks are bigger.

Northern Black Racer (Coluber constrictor). They are completely harmless and are among the most common and conspicuous snakes over much of South Carolina. Here's one from over on the Savannah River Site near Aiken. That snake looks nothing like a Cottonmouth.