Screaming or howling in Jackson County, Illinois

Me, my wife, and another hiking buddy (a female) had just hiked seven miles from the entrance of Red Cedar Trail, at Giant City State Park, to the primitive campsite where we set up our sleeping arrangements. My wife set her tent against the northwest part of the site. I was sleeping in a hammock and cocoon with a hammock tarp as my shelter southwest of her. My friend was also in a hammock/tarp southeast of my wife's tent. After setting up our sleeping arrangements, we started a fire with some fell wood that we found laying around the site. Once the fire was going good, we say down and reconstituted some dehydrated food that we hiked in. We drank tea and ate until our bellies were full. Afterward, me and my wife went to bed, while my friend stayed up and played on her phone. After a few minutes, she went to bed as well. To be perfectly transparent, I want to share a detail which may be of use to critics, but I know better as it relates to my story. Where I had my hammock, walnuts occasionally fell from the tree and hit my tarp and rolled off onto the campsite grounds. This was a common event and one I'm used to hearing as an avid hiker. I'm no novice to forest sounds and behaviors. The night progressed and the fire burned out. I remember poking my head out of the cocoon and looking at the fire to see how dim it was becoming. Because the campsite was so remote, I knew it would soon be pitch black. I remember a walnut falling the tree and striking my tarp. It rolled off into the darkness and found its resting spot. The fire grew dimmer and dimmer until I grew bored of watching it. I zipped myself within the cocoon and fell asleep. Sometime later, a loud thud woke from my sleep. "Maybe another walnut," I thought. Only it wasn't. It couldn't have been. Nothing ever hit the ground. Nothing rolled away off the of my pitched tarp. My heart raced. As I said before, I am an avid hiker/camper and I always look out of my hammock and under my tarp to see what's in the cap, but this time was different. I froze and couldn't move. It was like an involuntary fear that I've rarely experienced. I stayed that way until I calmed down, but never mustered the courage to look outside of my cocoon. The next morning, the first thing my wife tells me was that a bi-pedal creature was walking around her tent last night. My friend said, "Mine, too!" I tell them, "Something slapped my shelter." I go on to explain that it wasn't a walnut that fell on my tarp, because it never it hit the ground. My wife then tells us both that she heard two howls several minutes later and that they were about 15 minutes apart. According to her, the howl sound like a sign that paused at a very high pitch then broke into two small howls, then paused and two more small howls. That repeated itself another time. Me and my friend did not hear not, likely because we had fallen back to sleep. We left that campsite knowing we had an unexplainable experience. Although my friend is hesitant to believe it was the big guy, she does not deny that something with two legs was walking around her that night. As for me, I remain convinced that something slapped my tarp. My wife believes it was because I was a man, while her and my friend were female. Regardless, something with two legs entered our camp, in the dead of night, in pitch blackness, and left us unharmed, but fearful to look outside. We all shared that sense of fear and dread that we felt, but left the park not seeing the big guy, but at least two of us believing we were in close proximity to it.