If it's there and they can tax it they will. I've heard of full homes not being know about for years and then WHAM they find out about them and of course start taxing. At least normally there's no retro tax. You can always fight your taxes with the first method being an appeal when the valuation comes out. This is normally about April or May timeframe. That is if you think their valuation is over the real value of your home. You need to take evidence and support your value. That might be contracts from neighbors, CMAs from realtors, pictures of your house and others, maps and traffic counts, etc. If you are not comfortable doing this yourself there are often people that will fight for you. You can look at my website and click on the vendor link. There under tax you will find links to several firms that can help you fight your valuation.