>I'm drawing a blank, but was Tom Blankenship a real person?
>And where can I find out more about him?


Yes. From the autobiographical dictations:

"In Huckleberry Finn I have drawn Tom Blankenship exactly as he was ... I 
heard, four years ago, that he was justice of the peace in a remote village 
in Montana and was a good citizen and greatly respected."

-- Bob G.