There is another source to consult for enlistment and discharge records, The Report of the Adjutant General of the State of Indiana. It is not as detailed as the two sources I listed in the other post. This source shows in volume IV page 614 that William M. Parsons mustered in on September 12, 1861 and mustered out on September 1, 1864. The link to the page can be found at http://www.archive.org/stream/reportindiana04dougrich#page/614/mode/2up although I don’t know how well it will print out.

Tony