Home prices are still going down in many markets. But your property-tax bill might well be going up.

The good news: There are ways to fight back.

Property taxes across the U.S. have increased by nearly 20% from 2005 to 2009, the most recent data available, according to an April study by the National Association of Home Builders. The median annual real-estate-tax payment was $1,917 in 2009, up from $1,614 in 2005.

Over the same period, home prices in major urban centers fared badly, decreasing 31%, according to the Standard & Poor’s/Case-Shiller 20-City Composite Index.

There isn’t much you can do about your property-tax rate, which is set by your local government. But homeowners can often get their assessment lowered if they appeal to their local assessor.