The Sangamon County Historical Society does not maintain a research library.
All inquires about Sangamon County histories are referred to the Sangamon Valley Collection at Lincoln Library in Springfield, Illinois.  The SVC is the local history and genealogy collection for the city of Springfield and Sangamon County. 

Sangamon Valley Collection 
Lincoln Library 
326 S. Seventh St. 
Springfield, IL  62701 
217-753-4900 or email