A major change in Cook County’s taxable property classifications and assessments, along with the decline in home values in recent years, has many people wondering whether they should appeal their tax bills. The Civic Federation has a set of four documents that explain why and how to appeal in Cook County, all posted at http://civicfed.org/civic-federation/propertytax. But remember: Cutting your assessment won’t necessarily cut your tax bill. “It’s a zero-sum game,” says Lise Valentine, the group’s vice president and director of research. “It depends on how much your assessment went down in comparison to other people’s assessments.”