Tom just saw your PM, I should check these more often. You found yourself a coastal plains milksnake, a rare occurence above ground. I've seen dozens of this species but never once above the surface(not under cover) alive.
Corns and milks appear similar, not sure how to describe the differences. Corns are more red and yellow, different looking dorsal blotches too. You finding a milksnake just out and about is extremely rare, most people find them under cover.
corns have a telltale Y shaped mark extending from the top of the head part way down the neck and tend to have a blotchier pattern as opposed to stripes.I have never seen a coastal in the wild though I have found eastern milks in NY and WV.
When you told me that you had a corn snake on your recent hike in the Woodmansie vicinity, I thought that you were quite fortunate. I have photo documentation of a corn from near here that dates back a number of years. Now that I have seen your photo and read your ID-clinching words " It was black and white checkered underneath" I must concur with Dragoncjo that your snake is a coastal plain milksnake, not a corn snake. Still a good find and a fine photo! Let me suggest that you routinely try to take a photo of the underside next time. I don't think an active corn would allow you to do that without striking. Corns tend to have black tail stripes and black odd shaped polygons on their underside.
I've also asked my colleagues of Herpetological Associates, Inc., Matt McCort, Dave Schneider, and Bob Zappalorti to take a look at your photo. They concur with my identification.
Black racers have a solid grey belly while black rats have that type of belly so I imagine corns would too.I have never handled a wild corn but have handled and owned various morphs and while the coloration was different on these they all had the blotched belly.I also have a California Kingsnake and his belly is blotched too.I'd have to pull out the books to get a definite ID on belly patterns,I'm better with head scalation but if Chris says it's a milksnake and zappalorti too then it's a milsnake.Good ID pics of snakes are hard to come by because they seldom pose properly and most people snapping pics are in no way amenable to the idea of picking one up to get the proper shot.One way to tell milks and kings (basically the same type of snake) from rat snakes is rats have keeled scales and feel rough,kings and milks have smooth scales and feel smooth.Pines have keeled and so do hognose.Rattlers have keeled as well (Do not pick one up to see if it feels rough)
For the most part the dorsal blotches on a milk snake come closer down to the belly scales. Heads are different shapes too and the milk is less docile. The checkering can be absent on some coastals or minimal, corns are heavily checkered.