Here's a great comment left on my post titled One Positive of the Housing Decline that I thought you all would want to see:
My wife is a property tax assessor for our county, as well as a licensed appraiser at the state level. In our state, residences are reassessed every 3 years. The process is known as a "mass appraisal" because it has to be done at the neighborhood level (note that several "subdivisions" can make up a neighborhood. Quality of construction, square footage, land, and additions are some of the factors taken into account.
I don't recall the exact numbers, but in these mass appraisals, the goal (and state law) is that something like 90% of the homes should be within 10% of their "market value", that is, the price that the market would support if the property were sold in an arms-length transaction. In a year where market values are down over a three year span, the valuations of those homes being reassessed will be down. In a year where the market values are up over a three year span, the assessments will go up.
Also, due to the "average" nature of the mass appraisal, the chances of a property being undervalued are about the same as a property being overvalued. Of course, you don't hear of many people appealing their undervaluation. ;-)
While beastlike is correct about the budget being arrived at before tax rates are set, the assumption that the dollar amount of your taxes remains the same only applies if everyone in the county appealed their valuation when home values in the area drop.
The law is a bit tricky on this point -- Any property owner is required to file a "return" (think income tax return) each year during a certain window. This return simply allows you to state what you believe the property to be worth. The county can either accept your value or reject it. If they reject it, you have the right to appeal. If you do not file a return, the county's previous assessment becomes your automatic return. In essence, by failing to file a return, you are saying that you agree with the previously assessed value.
However, those homes that are up for their three year reassessment will be assigned a new value, and the property owners notified of the new assessment. These owners (one-third of the county each year) have the right to appeal their reassessment.
If you (a) did not file a return or (b) were not reassessed, then you have NO rights to appeal. This is the important part, at least in our state, and I would assume many others. If you believe the value of your home has dropped since your last assessment (or you believe a previous assessment was overvalued), FILE A RETURN. Otherwise you are stuck.
Mistakes made in square footage, additions, land, etc. are pretty much always corrected IF the process above is followed. If you come to an assessor after the windows have passed, their hands are pretty much tied. The values have been passed on to the county board at that point, and the budget will be set based on those values. The assessors cannot modify them after that point unless you filed a return (with a different value) or were reassessed in that year.
If you filed a return or were reassessed, and believe that you could not sell your property for the amount that you are assessed for, then you need to support that with reasonable comparisons of nearby, equivalent, arms-length transactions for the time period being appealed. For every appeal, my wife will research nearby transactions and see if they support the property owner's numbers. If they do, then she will go ahead and modify the assessment accordingly. It's understood that some percentage of the properties will be overvalued due to the nature of mass appraisals, and it's her responsibility to change these when they are brought to her attention.
Do NOT bring comparisons that are unrelated to your property--A father selling to a son, a foreclosed home, homes too far away from yours, vastly different square footages, vastly different acreages, etc. You are looking for comparisons that are "similar" to yours.
You can always sit down with the assessor and ask them for their comparisons. If you disagree with their comparisons, then you can appeal to the next step, in our state the Board of Equalization for the county. I would guess that your chances here depend on the quality of the assessor. If they know what they are doing, it's going to be hard for you to come up with better comparisons that convince the board that your valuation is better. For instance, my wife's valuations have been accepted over the property owner every single time in the last two years of appeals (about 40-50). Of course, she's also one of the few county assessors who is also a licensed appraiser.
If you lose before the Board of Equalization, you still have another option--you can appeal to the Superior Court. At this point there is a filing fee ($80?). My understanding is that the county attorneys do tend to settle a lot rather than go to court.
All said, it's going to take a lot of time and effort to argue an assessment that's close to the real value. If there are obvious mistakes, then you should absolutely appeal to have them corrected (make sure you file a return in order to do so). If you believe there is no way that you could sell the property for what the county's assessed value, then take that case to the assessor -- Chances are good that they will make the modifications if your numbers are reasonable. This is going to be the most likely course of action in this "down" market that we are currently seeing in most areas.
Regardless of what state you are in, now is probably the time to educate yourself on the process you need to follow next year to make sure your value is correct.