Your county assessor puts a value on your home each year using a mass-appraisal model. A separate board hears disputes. Here is how that split works.
Your county or local assessor decides your property's value each year. They run a mass-appraisal model that sweeps every home in the jurisdiction at once, then mail a notice showing what the model produced for yours. That number is what the tax bill is calculated from, whether or not it matches what your home would actually sell for.
Who is the assessor, and how do they do it?
The assessor is an elected or appointed local official whose job is to value every property in the jurisdiction on the same schedule, using the same method. In most counties, that method is mass appraisal: a statistical model pulling from recent sales, square footage, lot size, age, and condition codes. The assessor rarely visits individual homes. They update the model and run it.
The schedule varies. Some jurisdictions reassess every year, others every three to six years, and some use a rolling cycle where different neighborhoods get updated in different years.
What if you disagree with the number?
Every jurisdiction has a separate body that hears disputes over assessed value. It goes by different names in different places (Board of Equalization, Board of Review, Board of Revision, Board of Assessment Appeals), but the function is the same. An independent panel reviews the assessor's number against the evidence a homeowner brings.
The assessor does not decide appeals. The review board does. That separation is what makes the process work. If your value looks too high, the path is to file with that board inside the annual window.