The Illinois State Plane Coordinate System Committee (ISPCSC) has developed a collection of 33 zones tied to the North American Datum of 1983 (NAD 83).  This collection of zones is to be known as the “Illinois Coordinate System of 1983: 33 Zone layer” or “ICS83: 33 Zone”.  The individual ICS83: 33 Zone projections should be referred to as the “Illinois Coordinate System of 1983 {insert largest city in zone} Zone” or “ICS83-{largest city}”.  Example “Illinois Coordinate System of 1983 Freeport Zone” or “ICS83-Freeport”.  Distortion in the ICS83: 33 Zone layer is less than +20 ppm (0.10 feet per mile) between the grid and ground surfaces for 99% of the entire State of Illinois.  These 33 zones share the same boundaries as the zones intended for the eventual release of the North American Terrestrial Reference Frame of 2022 (NATRF2022).

The ICS83: 33 Zone layer will not be recognized or supported by the National Geodetic Survey (NGS) which means that it will not appear in any of their published geodetic tools.  For this reason, the ISPCSC has developed a custom conversion tool named ILCAT to easily transform data between NAD 83 projections.  For information on this tool see the ILCAT page.