Parts of Cook County have the taxable valuation of their homes reassessed every three years (PDF).
Last month the Cook County Assessor's office began mailing homeowners in Northern Cook County their "Notice of Proposed Assessed Valuation" that will affect 2010 taxes payable in 2011. Actual tax bills won't be known until the various taxing bodies set their rates.
Home buyers are aware that property values on the North Shore have been falling the past several years, but that's no guarantee that taxable assessed valuations will also fall. Even if they do, there may be little or no impact on the property taxes payable by an individual homeowner.
If property taxes are a major factor in your home purchase decision - and they ought to be since assessments can vary widely for similar properties - ask to see the Notice of Proposed Assessed Valuation in addition to checking the most recent tax bill. Also inquire whether the proposed valuation is under protest.