I’m new to the spider identification thing because I’m using it to get over my arachnophobia
but this is the first time Ive said this… i dont know
sorry for the bad answer maybe someone else can help
My guess is that this is a male orb weaver probably in the genus Araneus – but i don’t know which one. It may perhaps be a male Araneus marmoreus https://bugguide.net/node/view/1436448/bgimage
It also bears a resemblance to a male Araneus normanni but there is no listing on bugguide for A normanni in Illinois so i don’t know if it is present in your state.