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.

CHARLOTTE own Michigan Central Grand Rapids Division and Chicago & Grand Trunk Railroads 35 miles from Jackson 59 miles from Grand Rapids 26 miles from Battle Creek 112 miles from Detroit 18 miles from Lansing Population 3,500 County Seat of Eaton County Good Agricultural section iine Ash and Walnut Lumber region and Mercantile interests 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 W

There is no documentation I know of linking Mark Twain to his lecture in Lansing Michigan, December 23, 1868, but this site seems a good fit.

Interviewed "The Funny Men in Bed"  Detroit Post, 17 December 1884, p4  In "Mark Twain: The Complete Interviews" (#26)

Young Men s Hall on the north side of Jefferson Avenue between Bates and Randolph Streets was dedicated November 27 1850 It seated about 500 people and was the wonder and pride of the city for many years.

 The history of detroit and michigan or the metropolis illustrated, Silas Farmer, 1889

This was probably too small to be a venue for Twain.

I have no documentation that Mark Twain spoke here, but ...

Diefendorf Hall stands among a row of buildings along Main Street in the Village of Fort Plain. The building is historically significant for hosting Women’s Rights Movement leaders Susan B. Anthony and Elizabeth Cady Stanton in 1867. Stanton addressed the assembled audience on “Universal Suffrage.”

This site has not been specifically cited but based on dates opened this is likely the site visited by Mark Twain in 1868.

This was one of the legendary Newark showplace addresses at the busy corner of Halsey Street and Market Street. Opened in 1847, this location served 75 years of entertainment including live music, legitimate theatre, vaudeville, and movies. Beginning as Waller’s Opera House, Fred Waldmann took on the location changing it to Waldmann’s Opera House. The location would move to presenting vaudeville.

The Rondout Social Maennerchor was formed on February 22, 1868, by a handful of German immigrants who loved choral singing. They were drawn together by their common language, and love for music, singing, and social activities so that their clubhouse, "Washington Hall", became a gathering place for similar organizations up and down the Hudson River.

http://www.ghf-nj.org/Kingston.htm