A big city like Chicago is home to many ex-pats and, of course, the English are famous or infamous for exhibiting their culture abroad and sharing it with the natives...so don't be too surprised to find at least one celebration open to the public.
I would try stopping in for a beer at the
Red Lion Pub and asking one of the patrons or staff.
You might also search for British Pubs in Chicago and check their event schedules. On a quick search I found a car club that has an actual bonfire, but it may be for members only, so I won't post the details.
pd
Unchain your lunch money!