You need to use homes comparable to yours ("comps") located in the general area of your home to challenge your property taxes, not your entire zip code. If you have a Realtor you know, ask him or her to provide comps for your general neighborhood for you. If you don't want to ask your Realtor, you can do it yourself. Think of homes that sold in your neighborhood recently (the sales can be in 2009). With those addresses or the owners' names you can go on line to your local Assessor's/Auditor's Office website & obtain the info you want for each home.