99th Regiment, Ohio Infantry
The 99th Regiment was organized at Camp Lima, Allen County, Ohio, and mustered in August 26, 1862. It was consolidated with 50th Ohio Infantry December 31, 1864.
The Wikipedia article, 99th Ohio Infantry, gives a brief history of the unit, including places served, battles fought, and commanders.
Companies in the 99th Regiment with County of Origin
Larry Steven's Web site has a brief history of the 99th Regiment and a list of books, etc. for more information about the regiment.