Reference

• 
  BLM Illinois Public Land Survey System
• 
  Illinois Coordinate System of 1983 33-Zone System
• 
  Illinois County Boundaries, Polygons and Lines
• 
  Illinois PLSS Townships
• 
  Illinois Public Land Survey System (PLSS) Boundaries
• 
  Illinois State Boundary
• 
  Indian Treaty Boundary Lines
• 
  State Plane Zones
• 
  Universal Transverse Mercator (UTM) Zones
• 
  USGS Digital Raster Graphic (DRG) Files
• 
  USGS Digital Raster Graphic (DRG) Mosaic
• 
  USGS Quadrangle Boundaries and Corner Points in Illinois