In the summer of 2017, i was driving south on collins street in joliet, illinois and was approaching the intersection of cass street where i had planned to turn westbound. it was a fairly clear, sunny, cloudless day around 2:00 pm in the afternoon. i looked in the sky above collins street. about 2 blocks down, i saw a large white cube in the sky just hovering over collins street. as there was no good frame of reference it was difficult to say how high in the sky it was, but i would guess about 100 feet or so. it was also difficult to say how large it was, but it appeared to me to be about the size of a 2 or 3 story building and was a perfect cube in shape. i wondered if this was some kind of reflection or other issue, maybe regarding the windshield. so, i turned my head various directions and looked through different parts of the windshield to see if the cube changed in size, shape or location. it did not. the cube stayed in the sky at the same location, so i am fairly sure it had nothing to do with that. it just hovered there. as i turned onto cass at the intersection the cube just disappeared. even though i have looked for it in that location since that day, i have never seen it again.