The Plainfield-Guilford Township Public Library has published an online index (in PDF format) to its collection of Hendricks County insanity records. This collection - which is housed in the library's Indiana Room Archives - includes admittance papers, orders for discharge, witness affidavits, clothing requisitions, re-admittance papers, and others. What is interesting is reading what was considered "cause" for the person to be hospitalized or considered insane. Some of the described symptoms for women sound much like post-partum depression, something that wasn't treated in the 19th and early 20th centuries.
The insanity records range from the late 1850s to the 1920s. These records can be viewed in the library's Indiana Room upon request.