Marion County, IL
History
In 1790, the land of Marion county was still a part of the Northwest Territory.It was only 2 counties, St. Clair and St. Knox.
The land remained divided between the 2 counties until 1801. By 1813 the land was broken up into more counties and the land of Marion county was included in the new counties of Edwards, Jefferson, Crawford, and Fayette.
http://genealogytrails.com/ill/marion/history.html
Modern Day Adjacent Counties
Fayette County, IL - northClay County, IL - east
Wayne County, IL - southeast
Jefferson County,IL - south
Washington County, IL - southwest
Clinton County, IL - west
http://en.wikipedia.org/wiki/Illinois