In 2011, a group of house museums in the Chicago area formed a consortium called “At Home in Chicago.” Some of these houses are free to visit, while others cost admission. A list of the homes can be found here: http://www.chicagohousemuseums.org/directory/
Some of the homes that usually cost admission, occasionally have free days. The Cuneo Mansion in Vernon Hills, Illinois has free days on the second Saturday of each month (except in the winter months, when it is closed).

The Cuneo Mansion was completed in 1916 and belonged to an electrical pioneer named Samuel Insull, who was also the founder of the Chicago Civic Opera House in 1929. Unfortunately, he lost the house during the Great Depression.

Eventually, the home passed hands to the wealthy Cuneo family, who later donated it to Loyola University in Chicago in 2009. The University has hosted classes at the mansion, rented it out for events, and opened it up to the public for self-guided tours.

Although most house museums provide guided tours so that visitors can learn further information about the house, the self-guided tour option at the Cuneo Mansion was a nice change. I did not have to rush through the house, as I would on a formal tour, but could admire its beauty at my own pace. Because of the beauty of the home and grounds, Cuneo Mansion was apparently featured in a film with Julia Roberts called My Best Friend’s Wedding.
This mansion was probably built when Vernon Hills was less populated, however, it is now only five minutes away from Hawthorne Mall. When you arrive at the house’s gated entrance, be prepared to get out of your car and dial security with the phone there, so that they can lift up the front gate and let you in.

Sources and Further Reading
At Home in Chicago. http://www.chicagohousemuseums.org/ (accessed August, 31, 2019).
Cuneo Mansion. John A. Mallin. https://johnamallin.com/project/cuneo-mansion/ (accessed October 19, 2019).
Loyola Lake County Cuneo Mansion in Vernon Hills History. Loyola University Chicago. https://www.luc.edu/cuneo/mansion/ (accessed August, 31, 2019).
Loyola University Chicago Cuneo Mansion and Gardens Downloadable Tour. Loyola University Chicago. https://www.luc.edu/media/lucedu/cuneo/pdfs/cuneo-downloadabletour.pdf (accessed August, 31, 2019).