Thanks much for your reply! I went ahead and picked a couple quarts of the berries, and though their flavor is perhaps not as fine as that of wild Alaskan V. edule, I really don't think I'm dealing with the European opulus variety– all sources say that the drupes of V. opulus tend toward a bitter, medicinal taste and are considered all but inedible. One source I found just now has photos comparing the petiolar glands on the leaves of V. opulus & V. trilobum; I took a few complete leaves and stems with my picking, so that I could do an image search. I'll have to pull them out (put them in the fridge with the berries) in the morning to take a look at the glands. I feel pretty confident that I've got V. trilobum, though.
Someone clearly planted this particular shrub, but I see that the city of Chicago lists V. trilobum as a native species occurring within Jackson Park, which is not far away at all.