Download In State Plane Projection Here. This is our working version of the Lake County boundary. Although technically the county's eastern border extends eastward into Lake Michigan to the state line where Illinois meets Michigan, we routinely use the Lake Michigan shoreline as our eastern boundary for mapping purposes. The north, west and south boundaries are based on a compilation of survey data which aligns well, but not perfectly, with the border as mapped by neighboring counties and the State of Wisconsin, which forms the northern boundary of the county. Update Frequency: This dataset is updated on a weekly basis.