The location of Mark Twain's lecture in Akron, OH on December 30, 1868 is noted as the Methodist Church.  The location and name of the site in 1868 has not been definitively determined but one possibility is ...

The Universalist's Old Stone Church is gone, but the Sojourner Truth
Building in its place is named for an event that put Akron on the civil-rights map.

In 1811, Paul Williams settled near the corner of what is now Buchtel Avenue and Broadway. He suggested to General Simon Perkins, who was surveyor of the Connecticut Land Company's Connecticut Western Reserve, that they found a town at the summit of the developing Ohio and Erie Canal.

Although I have found no documentation on just where Mark Twain delivered his lecture, December 26, 1868, it seems likely it was somewhere within the historic district.

The Tecumseh Downtown Historic District is a historic district comprising the downtown commercial area of the city of Tecumseh in Lenawee County, Michigan. It was designated as a Michigan Historic Site on January 16, 1976 and added to the National Register of Historic Places on April 17, 1986.

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.