From the record
“The 5th District Appellate Court is located in Mount Vernon, Illinois, an incorporated town in Jefferson County. The building was originally constructed for the southern division of the Illinois Supreme Court, which was created by the 1848 Illinois constitution.”
Wikipedia article 5th District Appellate Court, CC BY-SA 4.0.
One of 2 National Register listings published here for Jefferson County · listed in 1973 · category: Building · built in 1854, Greek Revival architecture.
Sources: the Wikipedia article · the case file at the National Archives · the National Register database, National Park Service