There's a certain ambiguity about the date of the action in _Huck Finn_.  An
introductory note sets it "forty of fifty years ago," but given that the
was composed over many years, it is reasonable to stretch back as far as the
1820's and as near to the Civil War as the 1840's.  I think most people that
the later date is more accurate for the Mississippi River Valley that
in the novel.  You can't go far wrong calling it 1840.