Real Estate Taxes - Number of Homes or Properties
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The IRS instructions do not specify how many homes or properties you may include when deducting real estate taxes on Schedule A (Form 1040), Itemized Deductions. The only limitation appears to be that you cannot deduct on Schedule A the real estate taxes you paid for a property used for business. The taxes for business property would need to be deducted on the appropriate business form, if applicable.

To enter Form 1098, real estate (property) taxes paid, follow the steps in the Real Estate Taxes - Property Taxes FAQ. 
To enter Form 1098, Mortgage Interest Statement, follow the steps in the Form 1098 - Entering in Program FAQ.