Matthiessen State Park is near Utica and Oglesby, Illinois. It is also near Starved Rock State Park.
Frederick Williams Matthiessen developed the park for his personal use and after his death it was donated to the state of Illinois. It has since grown significantly in size.
There are two main areas that make up Matthiessen State Park: the Dells Area and the Vermillion River Area.
I ended up hiking a little under a mile. I forgot that unlike Indiana, Illinois kids had yet to start school. The park was packed and noisy. I will plan better next time so it will be a more peaceful adventure.