I have found no documentation linking Twain to this site but it does seem a good fit for his December 25, 1868 lecture:

SAMPSON HALL Size of stage 22 x24 Seating capacity 900 Eight sets of scenery Rent one night $15 two nights $25 three nights $30 one week $50 License 82 Will share with good attractions Address AH Sleater Manager or Homer Green Agent Seats sold at Western Union Telegraph Ofiice 

The plotted location is for the Eaton County Court House.  The actual location of Sampson Hall is unknown.