City of Elmhurst Zoning Code allows for a five foot setback on an interior sideyard to the eave. Chimneys may protrude into that setback up to 12 inches.
From the City of Elmhurst website:
Here is an example of a sideyard setback violation at 203 S West Avenue in which the foundation on the addition is 2 feet 10 inches from the lot line:
Here are 101 more that look suspiciously close to the lot line: