My property taxes have been paid by someone else for several years, they do not (can not) claim them. can i claim them. and if so, how many years could i go back

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To deduct property taxes, you must be an owner of the property against whom the taxes are assessed, and you must be the person who pays the taxes.   If the person who pays the taxes for you were to give you money, and you paid the taxes, that would work for the future, but if they pay them directly, you can't take a tax deduction.