The Government of Illinois, under the state’s constitution, has three branches of government: Executive, Legislative, and Judicial. The Executive Branch is split into several statewide elected offices, with the Governor as Chef Executive, and has numerous departments, agencies, boards and commissions. Legislative functions are granted to the General Assembly, a bicameral body consisting of the 118-member House of Representatives and the 59-member Senate. The judiciary is composed of the Supreme Court and lower courts.
The executive branch is composed of six elected officers and their offices as well as numerous other departments.  The six elected officers are:
The government of Illinois has numerous departments, agencies, boards and commissions, but the code departments, so called because they're established by the Civil Administrative Code of Illinois, provide most of the state's services:  
- Department on Aging
- Department of Agriculture
- Department of Central Management Services
- Department of Children and Family Services
- Department of Commerce and Economic Opportunity
- Department of Corrections
- Department of Employment Security
- Emergency Management Agency
- Department of Financial and Professional Regulation
- Department of Healthcare and Family Services
- Department of Human Rights
- Department of Human Services
- Department of Juvenile Justice
- Department of Labor
- Department of the Lottery
- Department of Natural Resources
- Department of Public Health
- Department of Revenue
- Department of State Police
- Department of Transportation
- Department of Veterans' Affairs
The Illinois General Assembly is the state legislature, composed of the 118-member Illinois House of Representatives and the 59-member Illinois Senate. The members of the General Assembly are elected at the beginning of each even-numbered year. Representatives elect from their chamber a Speaker and Speaker pro tempore, and senators elect from the chamber a President of the Senate.
The Governor has different types of veto like a full veto, reduction veto, and amendatory veto, but the General Assembly has the power to override gubernatorial vetoes through a three-fifths majority vote of each chamber. The General Assembly's session laws are published in the official Laws of Illinois.   The Illinois Compiled Statutes (ILCS) are the codified statutes of a general and permanent nature.  
The Supreme Court has limited original jurisdiction and has final appellate jurisdiction. It has mandatory jurisdiction in capital cases and cases where the constitutionality of laws has been called into question, and has discretionary jurisdiction from the Appellate Court. The Appellate Court is the court of first appeal for civil and criminal cases rising in the Illinois circuit courts.
The circuit courts are trial courts of original jurisdiction. There are 24 judicial circuits in the state, each comprising one or more of Illinois' 102 counties.  The circuit court has general jurisdiction and can decide, with few exceptions, any kind of case.
Springfield is designated as the Illinois capital. Many State of Illinois bureaucrats work in offices in Springfield, and it is the regular meeting place of the Illinois General Assembly.  All persons elected in a statewide manner in Illinois are required to have at least one residence in Springfield, and the state government funds these residences. 
As of 2014 [update] none of the major constitutional officers in the State of Illinois designated Springfield as their primary residence; most cabinet officers and all major constitutional officers instead primarily do their business in Chicago. A former director of the Southern Illinois University Paul Simon Institute for Public Affairs, Mike Lawrence, stated that many of the elected officials in Illinois "spend so little time in Springfield".  In 2012 St. Louis Post-Dispatch columnist Pat Gauen argued that because major state politicians such as the Governor of Illinois, as well as the Attorney General, Speaker of the House, the minority leader of the House, President of the Senate, the minority leader of the Senate, the Comptroller, and the Treasurer, all live in the Chicago area; because they work from the James R. Thompson Center in Chicago and that "Everybody who's anybody in Illinois government has an office in Chicago"; and because in March 2011 Governor Pat Quinn only spent a 68-day-40-night period in Springfield as per his official schedule, "in the reality of Illinois politics, [Springfield] shares de facto capital status with Chicago."  University of Illinois researcher and former member of the Illinois legislature Jim Nowlan stated "It’s almost like Chicago is becoming the shadow capital of Illinois" and that "Springfield is almost become a hinterland outpost."  Lawrence criticized the fact that state officials spent little time in Springfield since it estranged them from and devalued Illinois state employees based in that city. 
In 2007 Illinois state representative Raymond Poe criticized Illinois agency heads who commute to Springfield with state financing while maintaining their primary residences in the Chicago area. He sponsored House Bill 1959, which proposed ending state financing for travel to Springfield. 
According to Gauen, "Illinois seems rather unlikely to move its official capital to Chicago". 
The administrative divisions of Illinois are counties, townships, precincts, cities, towns, villages, and special-purpose districts.  Illinois has more units of local government than any other state—over 8,000 in all. The basic subdivision of Illinois are the 102 counties.  85 of the 102 counties are in turn divided into townships and precincts.   Municipal governments are the cities, villages, and incorporated towns.  Localities possess " home rule", which allows them to govern themselves to a certain extent.  Illinois counties, townships, cities, and villages may promulgate local ordinances.  Illinois also has several types of school districts (including the Chicago Public Schools and the Illinois Community College System) and additional units of government that oversee many other functions.
- Politics of Illinois
- Elections in Illinois
- Law of Illinois
- Law enforcement in Illinois
- Illinois Budget Impasse
- Uphoff, Judy Lee (2012). "The Governor and the Executive Branch". In Lind, Nancy S.; Rankin, Erik. Governing Illinois: Your Connection to State and Local Government (PDF) (4th ed.). Center Publications, Center for State Policy and Leadership, University of Illinois at Springfield. pp. 77–79. ISBN 978-0-938943-28-0. Archived from the original (PDF) on 2013-06-22. Retrieved 2013-11-30.
- 20 ILCS 5
- Smith, Lori L.; Barkley, Daniel C.; Cornwall, Daniel C.; Johnson, Eric W.; Malcomb, J. Louise (2003). Tapping State Government Information Sources. Greenwood Publishing Group. p. 126. ISBN 1-57356-387-0. LCCN 2002044846.
- "Illinois Legal Research Guide". University of Chicago Library. Retrieved 5 September 2013.
- Decker, John F.; Kopacz, Christopher (2012). Illinois Criminal Law: A Survey of Crimes and Defenses (5th ed.). LexisNexis. § 1.01. ISBN 978-0-7698-5284-3.
- Wojcik, Mark E. (2003). Illinois Legal Research. Carolina Academic Press. p. 38. ISBN 0-89089-339-X. LCCN 2003110318. OCLC 52972867.
- Gauen, Pat. " Illinois corruption explained: the capital is too far from Chicago " ( Archive). St. Louis Post-Dispatch. Retrieved on May 26, 2016.
- Reeder, Scott. " What does it cost taxpayers to pay for lawmakers’ empty Springfield residences?" ( Archive). Illinois News Network. September 11, 2014. Retrieved on May 26, 2016.
- " Committee votes to cut off funds for agency chiefs traveling here / Poe says capital is where they're supposed to be"[ dead link]. The State Journal-Register. March 15, 2007. Retrieved on May 26, 2016. Available on NewsBank, accessible from the newspaper archives. "State agency directors would no longer be reimbursed for travel expenses to Springfield under legislation a House committee approved Wednesday. "The state capital is Springfield, and that should be their work location," said Rep. Raymond Poe, R-Springfield, who sponsored House Bill 1959.[...]The Blagojevich administration has come under fire from lawmakers and others who question why many agency heads who live in the Chicago metropolitan area get travel expenses when they commute to the capital city."
- Individual State Descriptions: 2007 (PDF), 2007 Census of Governments, United States Census Bureau, November 2012, pp. 89–97
- Census 2007, p. 89.
- Illinois Regional Archives Depository System. "Name Index to Illinois Local Governments". Illinois State Archives. Illinois Secretary of State. Retrieved 11 November 2013.
- Gove, Samuel Kimball (1996). Illinois Politics and Government: The Expanding Metropolitan Frontier. Politics and Governments of the American States. University of Nebraska Press. pp. 155–156. ISBN 0-8032-7014-3. LCCN 95-46017.
- Gaylord, Tom (March 2007). "Finding Illinois Municipal Ordinances Online". Illinois Bar Journal. 95 (3): 156.