Sometimes on a corner lot, the tax assessor will show one address while the post office will show another. No biggie. The property that sits on the front of the lot should have a different pin.
If you have a real estate atty that you're working with, they can properly advise you about the grandfathering issue and will be able to pull a title search to check out pin #'s etc. Actually - if you submit an offer, all that "discovery" can be done during the atty review period. The seller should also be able to provide it too.
You can request a freedom of information request with the department of buildings. Simply fill out the form and request number of dwelling units. If the coach house has a kitchen and bathroom, it will be a dwelling unit. If the FOI comes back with a count that does not reconcile with the actual number, you will have to request a zoning opinion. It only needs to be "granfathered" in if current zoning does not allow for the coach house. Furthermore, just because it is allowed and noted, doesn't mean it doesn't have potential violations. The FOI can also request existing violations on a property. You can get the FOI from the Department of Buildings website.
I recommend working with an attorney familiar with zoning to help you with verification, if verification is possible. Best of Luck.
Keller Williams Chicago Consulting Group
Mary, I will go to the city hall and see what I can dig up. Ironically, the property has only one PIN no. However, the PIN no. description only reflected ONE property on the lot. Because this lot is larger than standard Chicago lot and the coach house has its own entrance on another street, I am thinking the assessors never really connected the two properties together when they verified the info. But when I did a search of the plat survey on the city and county site for that PIN, it includes the rear coach house when I saw the map.
Phillip, thank you for your suggestion. I will check the zoning office under the coach house's address and see what comes up for the zoning.
Thank you all for trying to help!
Be careful with couch houses. The city is trying to get rid of them whenever they can.