43rd Regiment, Illinois Infantry
The 43rd Regiment, Illinois Infantry was organized at Camp Butler, Illinois, and mustered in October 12, 1861. It mustered out November 30 and discharged at Camp Butler, Illinois, December 14, 1865. 
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.
Company F - many men from assorted counties - Roster, vol. 3, pages 257-260.
Company I - many men from the state of Ohio - Roster, vol. 3, pages 266-268.
Unassigned Recruits - Roster, vol. 3, pages 271-272.
Unassigned Drafted and Substitute Recruits - Roster, vol. 3, pages 272-273.
43rd Consolidated Infantry Regiment - Roster, vol. 3, pages 278-295 - Includes Companies A-K plus Unassigned Recruits.
- Civil War Soldiers and Sailors System, (accessed 30 Dec. 2010) can be searched by soldier's name or by regiment; includes regimental rosters and additional history of the regiment.
- Illinois Civil War Rosters from the Adjutant General's Report, 43rd Regiment (accessed 10 May 2011) includes rosters of all the regiments and information on the different companies in each regiment.
- National Park Service, The Civil War Soldiers and Sailors System, (accessed 10 May 2011).