I'm looking for any info on the ID of this tree. I'm in northern Illinois hardiness zone 5. Its not a common native tree in the area.
How familiar are you with this plant?
Is it on your property? Do you see it year round, through all four seasons? If so, when does it bloom, and what do the flowers look like? Does it set any kind of fruit? How about fall color?
With what appears to be opposite arrangement of simple leaves, it doesn't offer a lot of choices. You chose a non-representative branch (only new shoots) and gave a partial image of one leaf. We need more to ID this plant.
Take more pictures, and this time include older branch parts from which new shoots have grown. New/dormant buds will really help.
I was going to suggest an abnormally old specimen of Blackhaw Viburnum, but leaves/buds are not a match. I don't think this is really an opposite leaved plant, but only you can provide evidence. Some of those adventitious shoots on the trunk might be helpful, but I also think additional images of the branches will be useful too.
Any images of flowers, fruit, etc. will be good too. That tree has distinctive bark; we should be able to solve this with more information.
Furrowed bark is characteristic of certain ash species, as are opposite leaflets. Maybe it's one of them.
Fraxinus americana (white ash) perhaps.
I could follow nel5397's line of thinking with Euonymus sp. - which would not be native nor common.
That plant could fit with one of the exotic introductions that can reach significant trunk diameter and tree size. Again: more information and better images will help.
Here's a link to a recent discussion of various odd Spindles: