Per Alan Dornfest, Property Tax Policy Supervisor for the Idaho State Tax Commission:
Taxes are not tied directly to home values, despite what a lot of people think. Taxes are based on the budgets of taxing districts. If cities, counties, and other taxing districts budget the same amount from property tax from one year to the next, but property values go down, the levy rate goes up automatically to compensate.
For most taxing districts, budgets aren't set until August or early September, so final property tax amounts won't be certain until then. Dornfest said property values are determined by county assessors as of January 1 of each year, so whatever happens to the real estate market later in the year has no impact until the following year's assessment. While property values have plummeted in some parts of Idaho during 2009, Dornfest said, they've actually risen in others.
The Tax Commission oversees Idaho's property tax system, which is administered by the counties. For more information on property assessments and taxes, visit the Property Tax section of the Tax Commission's website.