Suburban homeowners not getting break, either

Residential neighborhoods in Deerfield, Highland Park and other parts of southern Lake County are seeing soaring property assessments.

The same is true for residential areas of Naperville in DuPage and Will counties, parts of Kane County near Geneva and St. Charles, and fast-growing areas around Bolingbrook, New Lenox and Frankfort in Will County.

Assessments are done differently in the collar counties than in Cook County, but the numbers still are heading steadily upward.

Residential property assessments across the five collar counties rose at least 5 percent on average in 2006, according to county and township officials. Assessments varied dramatically within each county, with some neighborhoods or townships registering increases of 10 percent to 15 percent.

Outside of Cook County, residential properties are assessed for tax purposes at one-third of their market value. And virtually everywhere, the assessments are recalculated annually in an effort to keep the numbers current and smooth out sharp increases. That doesn't prevent big jumps in some areas.

Property or market values -- which form the basis for assessed valuation -- are influenced by everything from the location to the number of houses in the area for sale and even inflation, officials said.