Counties are the primary legal divisions in Illinois.
U.S. Census Bureau, Geography Division. Geographic Terms and Concepts – County or Statistically Equivalent Entity.
Number of counties and yearly changes in counties: There are 102 counties in Illinois. The number of counties has remained stable since the middle of the 19th century.
Data availability by county: The county is the principal geographic region for presentation of data on IECAM. All site-based data (e.g., child care), most non-site-based data (e.g., early intervention), and almost all demographic data (e.g., population) are presented by county.