Sometimes this is hard to tell. You would have to live in an unincorporated area (not technically in Village of Bensenville or the City of Elmhurst) between Elmhurst and Bensenville, in DuPage County and Addison Township.
One good clue is whether or not you vote for Bensenville or Elmhurst candidates. Another good clue is if you have a letter in the middle of your address, which indicates that you live in an unincorporated area. One way to be certain is if your property tax bill has a line for “Bensenville Fire Protection District #1”.