42nd Regiment, Illinois Infantry
The 42nd Regiment, Illinois Infantry was organized at Chicago, Illinois, July 22, 1861. It mustered out at Camp Irwin December 16 and discharged at Springfield, Illinois, January 10, 1866. 
For more information on the history of this unit, see:
The Civil War Archive section,42nd Regiment Infantry, (accessed 14 June 2012).
The Wikipedia article, 42nd Illinois Volunteer Infantry Regiment, (accessed 15 June 2012).
Companies in this Regiment with County 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 following counties of origin are taken from the Adjutant General's Report, found on the Illinois Civil War Rosters web site. Roster pages are from the same report found on the Internet Archives web site. The rosters show the men who served in each regiment, their residences, dates of enlistment and mustering out, and other remarks.
Veteran Battalion - 42nd Regiment - Companies A-C - Roster, vol. 3, pages 200-204. (Includes Unassigned men from each Company.)
Company E - many men from the state of Michigan - Roster, vol. 3, pages 220-223.
Company F - many men from the state of Michigan - Roster, vol. 3, pages 223-226.
Unassigned Recruits - Roster, vol. 3, pages 240-241.
- 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 ‘Illinois 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.
- Illinois in the Civil War describes many Confederate and Union sources, specifically for Illinois, 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, Part 1 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.
- Illinois Civil War Rosters from the Adjutant General's Report, 42nd Regiment (accessed 10 May 2011) includes rosters of all the regiments and information on the different companies in each regiment.
- Illinois State Archives - Illinois Civil War Muster and Descriptive Rolls Database (accessed 14 June 2011). Search by residence, unit, regiment, company or soldier.
- The ILGenWeb Civil War Scrapbook, (accessed 9 Aug 2011) contains links to various documents such as personal letters, military papers, articles, histories, obituaries, biographies, etc. Documents are listed by regiment, then by the soldier and his company.
- National Park Service, The Civil War Soldiers and Sailors System, (accessed 10 May 2011).