Counties were originally created to fulfill administrative functions for the state. Over the past severl decades, the role of counties in Illinois has undergone several changes, due in large part to the adoption of the 1970 Illinois Constitution. The administrative structure of county government was modified, as well as the percentage of tax revenue counties could retain from local government taxes. Counties still serve as an arm or extension of the state, operating the courts and jails, the state attorney's office, and the office of the public defender. The state shares its income and sales tax with counties to help counties carry out these functions. In addition to the shared revenue, the state also provides a partial funding for the cost of running courts and provides grants for health care.
Other important functions of Illinois' 102 counties are to collect the property tax, maintain public health systems, administer the judicial system and conduct most elections. In unincorporated areas, counties maintain county roads and bridges and provide law enforcement. Counties are increasingly becoming involved in consumer protection, regional economic development, and utility regulation.
Counties are organized into one of two basic forms of government, with slightly different duties. In counties organized with townships, the townships are responsible for General Assistance, property assessment, and road and bridge maintenance. In counties organized without township government, [called commission counties] the county government performs traditional township functions including tax assessment and general assistance, while road districts typically perform road construction and maintenance. There are 85 counties in Illinois with townships and 17 counties operating on a commission basis. The latter are generally located in the southern and western parts of the state.