123rd Regiment, Ohio Infantry
The 123rd Regiment was organized at Monroeville, Ohio, and mustered in September 24, 1862. It had duty in the Department of Virginia until June and mustered out June 12, 1865. 
For more information on the history of this unit, see:
- The Civil War Archive section, 123rd Regiment Infantry, (accessed 5 September 2012).
- Larry Stevens' Ohio in the Civil War web page for the 123rd Ohio Infantry.
Companies in this Regiment with the Counties of Origin
Men often enlisted in a company recruited in the counties where they lived though not always. After many battles, companies might be combined because so many men were killed or wounded. However if you are unsure which company your ancestor was in, try the company recruited in his county first.
The above information is from The Military History of the 123d Regiment of Ohio Volunteer Infantry, edited by Charles M. Keyes (see above), pages 6-25. Digital version on Internet Archive.
A county listing from C.M. Keyes' The Military History of the 123d Regiment, Ohio Volunteer Infantry is also on Larry Stevens' Ohio in the Civil War web page for the 123rd Ohio Infantry.
- Beginning United States Civil War Research gives steps for finding information about a Civil War soldier. It covers the major records that should be used. Additional records are described in ‘Ohio in the Civil War’ and ‘United States Civil War, 1861 to 1865’ (see below).
- National Park Service, The Civil War Soldiers and Sailors System, is searchable by soldier's name and state. It contains basic facts about soldiers on both sides of the Civil War, a list of regiments, descriptions of significant battles, sources of the information, and suggestions for where to find additional information.
- Ohio in the Civil War describes many Confederate and Union sources, specifically for Ohio, and how to find them.. These include compiled service records, pension records, rosters, cemetery records, Internet databases, published books, etc.
- United States Civil War, 1861 to 1865 describes and explains United States and Confederate States records, rather than state records, and how to find them. These include veterans’ censuses, compiled service records, pension records, rosters, cemetery records, Internet databases, published books, etc.
- Keyes, Charles M., ed. The Military History of the 123d Regiment of Ohio Volunteer Infantry. Sandusky, Ohio: Register Steam Press, 1874. 196 p. Google Books. FHL Collection fiche 6118273 (3 fiche) and (Washington [District of Columbia] : Filmed by the Library of Congress Photo duplication Service, 1987) FHL Film 1550151.
- Snyder, Edwin. Adventures and misadventures, civil and military, of a Union veteran of the Civil War. (Bethesda, Maryland : University Publications of America, c1993) FHL Fiche 6118274
- National Park Service, The Civil War Soldiers and Sailors System, (accessed 6 December 2010). &amp;amp;amp;lt;br&amp;amp;amp;gt;