Somerset is an ancient county which having been combined with Avon,  in 1974 is now back in a Countyin it's own right.

The Somerset flag which is commercially available and is widely flown show a dragon rampant on a white background.

The dragon looks rather suspiciously like a Wessex Wyvern and may have it's roots in that symbol.

There is some discussion over this flag which you can see on this youtube clip