Lake County Illinois GISDownload In State Plane Projection Here . Municipal boundaries are based on annexations, court orders and other legal documents filed in the office of the Recorder of Deeds. Mapping is based on the legal descriptions from those documents, which relate to existing parcel boundaries or to the underlying PLSS. Important attributes include "Type" which contains an "I" if the polygon represents an incorporated area, and a "U" if unincorporated. The municipality name for "I" type polygons is included in the attribute "NAME1." Update Frequency: This dataset is updated on a weekly basis.ArcGIS FeatureLayerhttps://hub.arcgis.com/datasets/811621907d3649778ef35ec37731e921_10engLake County Illinois Open Data PortalPublicMunicipal Boundaries [Illinois--Lake County]Web servicesIllinois--Lake CountyIllinoisLast Modified: 2026-01-04