Thanks for the information about the 12th Cavalry as likely suspects in the burning of Dallas. I've come across two other possibilities:

1) Soldiers of the 13th Illinois Cavalry Regiment in September, 1862. My source is Geraldine Sanders Smith, in "Civil War Times in Madison County, Missouri, and Surrounding Counties" (St. Louis, Mo. Self-published, 1999), p. 103. She, in turn, cites her source as "History of the Thirteenth Cavalry Regiment (1888)."

2) The 24th Illinois Volunteer Infantry Regiment--aka the 1st Hecker Jaeger Regiment--which for a time operated in Southeast Missouri in connection with Grant's 21st Illinois. The regiment was led by Col. Frederich Hecker. The basis for this conjecture appears on page 139 of Silvana R. Siddali's "Missouri's War: The Civil War in Documents," in which she cites a letter written by David Allan, a private in the 29th Regiment Infantry Volunteers:

"Saturday Nov 15/62... Passed through Dallas now deserted by all of its inhabitants except two or three women. The houses are all more or less destroyed, some being burnt to the ground. This place was a regular den of secessioners and last springer Hecker cleaned out the crew and destroyed their property."

Of course, it is possible that Private Allan's meaning was that Hecker destroyed only certain property belonging to "secessioners" and not the entire town.

Southeast Missouri State University Press is evaluating for possible publication a historical novel that my grandfather wrote about the war in Bollinger County, based to a considerable degree on the experiences of his father and an uncle in a local militia company led by Capt. John R. Cochran. I've added a number of appendicies to the novel, including one about how Dallas fared during the war, in which I cite the above information. If SMSU Press decides to accept the book for publication, I'd like to add your information about another possible explanation for the town's burning.

Best wishes

George Williams