Taxes are paid annually in arrears. So the 2009 tax bill doesn't come out until the fall of this year. The value is based on the county assesment as of January 1. They are not permitted by law to use values from 2008, it must be the properties value on January 1 of 2009.
Once you receive your bill the instructions are on there telling you what to do to appeal it if you don't agree with the value. You are given a nice discount if you pay them in November.