Held at Indiana University's Archives (description and partial document below):
ORDERLY BOOK OF THE LEXINGTON LIGHT INFANTRY
"An orderly book is a record book kept by a military company in which general and regimental orders are recorded. This orderly book belonged to a company that fought at the River Raisin [link added]... ."
The Indiana Genealogical Society has more about the Orderly Book in its publication here.